---
kind: "section"
citation: "10 U.S.C. § 949k"
title: "10"
title_heading: "Armed Forces"
number: "949k"
heading: "Defense of lack of mental responsibility"
release: "119-102"
date: "2026-07-12"
url: "https://uscodex.org/usc/10/949k"
units:
  - "Subtitle A — General Military Law"
  - "Part II — Personnel"
  - "Chapter 47A — Military Commissions"
  - "Subchapter IV — Trial Procedure"
---

# §949k. Defense of lack of mental responsibility

- (a) **Affirmative Defense.—** It is an affirmative defense in a trial by [military](/usc/10/801.md?p=8) commission under this chapter that, at the time of the commission of the acts constituting the offense, the accused, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of the acts. Mental disease or defect does not otherwise constitute a defense.
- (b) **Burden of Proof.—** The accused in a [military](/usc/10/801.md?p=8) commission under this chapter has the burden of proving the defense of lack of mental responsibility by clear and convincing evidence.
- (c) **Findings Following Assertion of Defense.—** Whenever lack of mental responsibility of the accused with respect to an offense is properly at issue in a [military](/usc/10/801.md?p=8) commission under this chapter, the [military judge](/usc/10/801.md?p=10) shall instruct the members as to the defense of lack of mental responsibility under this section and shall charge the members to find the accused—
  - (1) guilty;
  - (2) not guilty; or
  - (3) subject to [subsection (d)](#d), not guilty by reason of lack of mental responsibility.
- (d) **Majority Vote Required for Finding.—** The accused shall be found not guilty by reason of lack of mental responsibility under [subsection (c)(3)](#c-3) only if a majority of the members present at the time the vote is taken determines that the defense of lack of mental responsibility has been established.

## Source credit

(Added Pub. L. 111–84, div. A, title XVIII, § 1802, Oct. 28, 2009, 123 Stat. 2588.)

## Notes

### Editorial Notes

### Prior Provisions

A prior section 949k, added Pub. L. 109–366, § 3(a)(1), Oct. 17, 2006, 120 Stat. 2615, related to the defense of lack of mental responsibility, prior to the general amendment of this chapter by Pub. L. 111–84.