18 U.S.C. § 17
Section 17 · Insanity defense
Amended 2 times on record
Applied in 318 court decisions — leading case Penry v. Lynaugh (1989)
Most recently applied in Hanan Khashoggi v. NSO Group Technologies Limited (May 2025)
Applied most in the Ninth Circuit Circuit (26 decisions)
Cases citing this section usually also cite 18 U.S.C. § 4241 · 18 U.S.C. § 924 · 18 U.S.C. § 922
How often courts cite this section
Court decisions citing this, by year.Markers show enactment, consequential amendments, and circuit splits over this section — watch for a citation surge after a change or a disagreement. The dip in the last several years is a data-coverage gap, not a real trend — our corpus holds fewer opinions from the most recent years, so recent citations are undercounted.
(a) Affirmative Defense.—It is an affirmative defense to a prosecution under any Federal statute that, at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense.
(b) Burden of Proof.—The defendant has the burden of proving the defense of insanity by clear and convincing evidence.