A VA disability rating can rest on a condition that began in service. It can also rest on a later condition that is tied to one VA has already service-connected. That second path is secondary service connection. The regulation that states it is 38 C.F.R. § 3.310. The statutes that authorize the compensation are 38 U.S.C. § 1110 (wartime service) and 38 U.S.C. § 1131 (peacetime service).
This page quotes those sources. It is not a promise of a grant, a rating, or a particular effective date. It is not a list of conditions that “always” qualify. Except for the two situations § 3.310 itself holds to be the proximate result of a listed service-connected injury — certain cardiovascular disease after specified amputations, and certain conditions after service-connected traumatic brain injury — secondary service connection is decided on the evidence in the file.
The Jacks Law Group represents veterans in VA disability claims, veterans appeals, and related VA benefits.
The regulation
38 C.F.R. § 3.310 is titled “Disabilities that are proximately due to, or aggravated by, service-connected disease or injury.” Paragraph (a) is the general rule:
“Except as provided in § 3.300(c), disability which is proximately due to or the result of a service-connected disease or injury shall be service connected. When service connection is thus established for a secondary condition, the secondary condition shall be considered a part of the original condition.”
38 C.F.R. § 3.310(a).
The exception named in that sentence is 38 C.F.R. § 3.300(c). For claims for secondary service connection received by VA after June 9, 1998:
“a disability that is proximately due to or the result of an injury or disease previously service-connected on the basis that it is attributable to the veteran's use of tobacco products during service will not be service-connected under § 3.310(a).”
38 C.F.R. § 3.300(c).
The statutes
Wartime basic entitlement is 38 U.S.C. § 1110:
“For disability resulting from personal injury suffered or disease contracted in line of duty, or for aggravation of a preexisting injury suffered or disease contracted in line of duty, in the active military, naval, air, or space service, during a period of war, the United States will pay to any veteran thus disabled and who was discharged or released under conditions other than dishonorable from the period of service in which said injury or disease was incurred, or preexisting injury or disease was aggravated, compensation as provided in this subchapter, but no compensation shall be paid if the disability is a result of the veteran's own willful misconduct or abuse of alcohol or drugs.”
Peacetime basic entitlement is 38 U.S.C. § 1131. The text is the same except that it applies “during other than a period of war.” The Federal Circuit treats the two statutes as otherwise identical. Spicer v. McDonough, 61 F.4th 1360, 1361 n.1 (Fed. Cir. 2023) (citing Gilpin v. West, 155 F.3d 1353, 1356 (Fed. Cir. 1998)).
The words that control the causal standard are “disability resulting from.”
What “resulting from” means after Spicer
In Spicer v. McDonough, 61 F.4th 1360 (Fed. Cir. 2023), the Federal Circuit construed 38 U.S.C. § 1110. The official opinion is dated March 8, 2023. The veteran had service-connected leukemia. Knee-replacement surgery was canceled because leukemia medication kept his hematocrit too low for surgery. The Board had said that an inability to have surgery because of a service-connected disease was not secondary service connection. The Federal Circuit vacated and remanded.
The court held that “resulting from” in § 1110 is but-for causation, and that but-for causation is broader than proximate causation:
“The parties also agree that the language ‘resulting from' in § 1110 requires but-for causation. … The parties further agree that but-for causation is a broad standard of causation, or at least broader than proximate causation, and encompasses multi-link causal chains.”
Spicer, 61 F.4th at 1364.
“No textual or contextual indication dictates a narrower interpretation of ‘resulting from' than but-for causality. … Stated otherwise, but-for causation is broad, undisputedly broader than proximate cause. … Thus, the causation standard of § 1110 is simply standard but-for causation.”
Id. at 1365.
“Put together, § 1110 plainly requires compensation when a service-connected disease or injury is a but-for cause of a present-day disability. This broad language applies to the natural progression of a condition not caused by a service-connected injury or disease, but that nonetheless would have been less severe were it not for the service-connected disability. Stated another way, § 1110 provides for compensation for a worsening of functionality—whether through an inability to treat or a more direct, etiological cause. Nothing in the statute limits § 1110 to onset or etiological causes of a worsening in functionality.”
Id. at 1365–66.
The court decided the case on the statute. It then said this about the aggravation regulation:
“We decide this case based on our interpretation of § 1110 alone. To the extent that the VA also applied 38 C.F.R. § 3.310(b) to reject Mr. Spicer's theory of compensation, that regulation is unlawful as inconsistent with 38 U.S.C. § 1110.”
Id. at 1367.
That is the holding. This page does not say that § 3.310 was repealed. Cornell LII still prints § 3.310(a)–(d), retrieved August 16, 2026. The Federal Circuit held that § 3.310(b) may not be used to reject a claim that fits § 1110's but-for standard, including a claim that a service-connected disease or injury impeded treatment of another disability.
This page does not quote an M21-1 revision. That manual was not opened for this draft. Third-party descriptions of a May 2026 manual change are not used as law.
Aggravation, as the regulation still prints it
38 C.F.R. § 3.310(b), as retrieved on August 16, 2026, still reads:
“Any increase in severity of a nonservice-connected disease or injury that is proximately due to or the result of a service-connected disease or injury, and not due to the natural progress of the nonservice-connected disease, will be service connected. However, VA will not concede that a nonservice-connected disease or injury was aggravated by a service-connected disease or injury unless the baseline level of severity of the nonservice-connected disease or injury is established by medical evidence created before the onset of aggravation or by the earliest medical evidence created at any time between the onset of aggravation and the receipt of medical evidence establishing the current level of severity of the nonservice-connected disease or injury. The rating activity will determine the baseline and current levels of severity under the Schedule for Rating Disabilities (38 CFR part 4) and determine the extent of aggravation by deducting the baseline level of severity, as well as any increase in severity due to the natural progress of the disease, from the current level.”
VA added that paragraph after Allen v. Brown, 7 Vet. App. 439 (1995). In the 1997 proposed rule, VA recited the Allen holding this way:
“In Allen v. Brown, 7 Vet. App. 439, 448 (1995), issued March 17, 1995, CVA held that, as a matter of law, when aggravation of a veteran's nonservice-connected condition is proximately due to or the result of a service-connected condition, the veteran is entitled to compensation for the degree of disability (but only that degree) over and above the degree of disability existing prior to aggravation.”
62 Fed. Reg. 30547 (June 4, 1997).
Read together with Spicer: the statute requires compensation when a service-connected disease or injury is a but-for cause of present-day disability, including a worsening of functionality or an inability to treat. The printed text of § 3.310(b) still describes a baseline-and-deduction method for rating the increase. Spicer held that § 3.310(b) is unlawful as inconsistent with § 1110 to the extent VA used it to reject a but-for / inability-to-treat theory. This page does not collapse those two sentences into one rule, and it does not invent how a particular rater will apply them on a particular claim.
Two situations the regulation itself treats as the proximate result
#### Cardiovascular disease after specified amputations
38 C.F.R. § 3.310(c):
“Ischemic heart disease or other cardiovascular disease developing in a veteran who has a service-connected amputation of one lower extremity at or above the knee or service-connected amputations of both lower extremities at or above the ankles, shall be held to be the proximate result of the service-connected amputation or amputations.”
That sentence is limited to the amputations it names. It is not a general heart-disease presumption.
#### Traumatic brain injury
38 C.F.R. § 3.310(d)(1) states that, in a veteran who has a service-connected traumatic brain injury, the following “shall be held to be the proximate result of the service-connected traumatic brain injury (TBI), in the absence of clear evidence to the contrary”:
“(i) Parkinsonism, including Parkinson's disease, following moderate or severe TBI;
(ii) Unprovoked seizures following moderate or severe TBI;
(iii) Dementias of the following types: presenile dementia of the Alzheimer type, frontotemporal dementia, and dementia with Lewy bodies, if manifest within 15 years following moderate or severe TBI;
(iv) Depression if manifest within 3 years of moderate or severe TBI, or within 12 months of mild TBI; or
(v) Diseases of hormone deficiency that result from hypothalamo-pituitary changes if manifest within 12 months of moderate or severe TBI.”
38 C.F.R. § 3.310(d)(2) then keeps the general rule open:
“Neither the severity levels nor the time limits in paragraph (d)(1) of this section preclude a finding of service connection for conditions shown by evidence to be proximately due to service-connected TBI. If a claim does not meet the requirements of paragraph (d)(1) with respect to the time of manifestation or the severity of the TBI, or both, VA will develop and decide the claim under generally applicable principles of service connection without regard to paragraph (d)(1).”
Paragraph (d)(3) defines mild, moderate, and severe TBI for this section by structural imaging, loss of consciousness, alteration of consciousness, post-traumatic amnesia, and Glasgow Coma Scale, “based on the TBI symptoms at the time of injury or shortly thereafter, rather than the current level of functioning.” 38 C.F.R. § 3.310(d)(3)(ii).
Direct service connection is a different finding
Secondary service connection starts from a condition that is already service-connected. Direct service connection is the finding that the disability itself was incurred or aggravated in service. 38 C.F.R. § 3.303(a) states:
“Service connection connotes many factors but basically it means that the facts, shown by evidence, establish that a particular injury or disease resulting in disability was incurred coincident with service in the Armed Forces, or if preexisting such service, was aggravated therein. … Determinations as to service connection will be based on review of the entire evidence of record, with due consideration to the policy of the Department of Veterans Affairs to administer the law under a broad and liberal interpretation consistent with the facts in each individual case.”
A claim can be developed on more than one theory. This page is about the secondary path in § 3.310 and the statutory “resulting from” standard in §§ 1110 and 1131.
What this page does not do
It does not list unofficial “common secondary pairs” as if they were presumptions. Except for § 3.310(c) and § 3.310(d)(1), the regulation does not name a condition as automatically secondary.
It does not treat a bill as law. No 119th Congress bill is used as a source here.
It does not treat an unopened M21-1 paragraph as the rule. The opened sources are the statute, the regulation, Spicer, and VA's published recitation of Allen.
It does not promise a result. Board and court decisions apply these texts to a record. A different record can produce a different result.
How to reach the firm
If you want to talk through a VA disability decision, a secondary-condition claim, or an appeal, call The Jacks Law Group at 702-834-6300 or visit https://www.TheJacksLawGroup.com.
The Jacks Law Group 1057 Whitney Ranch Drive, Suite 350 Henderson, NV 89014 702-834-6300 https://www.TheJacksLawGroup.com