New York Consolidated Laws

N.Y. Penal Law § 40.15 (2026)

Mental disease or defect

✓ current as of May 2026

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§ 40.15 Mental disease or defect.
  In any prosecution for an offense, it is an affirmative defense that
when the defendant engaged in the proscribed conduct, he lacked criminal
responsibility by reason of mental disease or defect. Such lack of
criminal responsibility means that at the time of such conduct, as a
result of mental disease or defect, he lacked substantial capacity to
know or appreciate either:
  1. The nature and consequences of such conduct; or
  2. That such conduct was wrong.

Notes of Decisions

Cited in 177 cases (19 in the last 5 years), 1985–2026 · leading case: People v. Kohl, 527 N.E.2d 1182 (NY 1988).

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People v. Kohl, 527 N.E.2d 1182 (NY 1988). · cites it 11× “10), and indicated that he would assert the affirmative defense of mental disease or defect (Penal Law § 40.15). At the bench trial, the prosecution at first concentrated on the factual developments by testimony of the eyewitnesses.”

People v. Tortorici, 709 N.E.2d 87 (NY 1999). · cites it 4× “On December 29, 1995, in order to rebut the defense that defendant was not responsible for his actions by reason of mental disease or defect ( see , Penal Law § 40.15), the People moved for an order directing defendant to submit to an examination pursuant to CPL 250.”

People v. Almonor, 715 N.E.2d 1054 (NY 1999). · cites it 5× “On May 12, 1997, just before jury selection, defendant revealed for the first time that on retrial he intended to pursue a Penal Law § 40.15 insanity affirmative defense, and, in addition, a psychiatric defense based on his inability to form an assaultive intent.”

People v. Wilhelm, 34 A.D.3d 40 (N.Y. App. Div. 2006). · cites it 2× “Thus, the only issue concerning defendant’s criminal responsibility in this case involved her substantial capacity to know or appreciate that her conduct was wrong, which defendant bore the burden of establishing by a preponderance of the evidence (see Penal Law § 40.15; People…”

People v. Gilbert, 2021 NY Slip Op 06003 (N.Y. App. Div. 2021). · cites it 9× “During the ensuing jury trial, defendant raised the affirmative defense of lack of criminal responsibility by reason of mental disease or defect ( see Penal Law § 40.15), emphasizing that she had a mental illness and, at the time of the killing, did not appreciate the nature and…”

People v. Goldstein, 843 N.E.2d 727 (NY 2005). · cites it 2× “The only issue at trial was whether defendant had established, by a preponderance of the evidence, his affirmative defense that he should not be held criminally responsible for his conduct because he suffered from a mental disease or defect at the time of the killing ( see Penal…”

People v. Lancaster, 503 N.E.2d 990 (NY 1986). · cites it 2× “1, 1984, reenacted as an affirmative defense Penal Law § 40.15). 3 Defendant was indicted for *24 attempted murder in the second degree (Penal Law §§ 110.”

People v. Kot, 126 A.D.3d 1022 (N.Y. App. Div. 2015). · cites it 4× “Thus, it cannot be said that there is a "reasonable probability" (People v McKnight, 306 AD2d 546, 548 [2003], lvs denied 100 NY2d 593 , 596, 599 [2003]) that the jury, had it heard Houghtalen testify in support of a theory of insanity under Penal Law § 40.15, would have instead…”

People v. Smith, 217 A.D.2d 221 (N.Y. App. Div. 1995). · cites it 3× “The primary defense was that defendant lacked criminal responsibility by reason of mental disease or defect (see, Penal Law § 40.15). The defense put on a number of lay and expert witnesses who testified about defendant’s physical, developmental, intellectual, and emotional…”

People v. Horan, 290 A.D.2d 880 (N.Y. App. Div. 2002). · cites it 2× “Some months later, the same psychiatrists found defendant competent to stand trial, a determination shared by the prosecution and defense expert psychiatrists who were retained by each side to evaluate defendant and to testify at trial regarding defendant’s defense of mental…”

People v. Marlett, 2021 NY Slip Op 01164 (N.Y. App. Div. 2021). · cites it 2× “A jury found defendant guilty of all charges, rejecting his affirmative defense of lack of culpability by reason of mental disease or defect ( see Penal Law § 40.15). At sentencing, Supreme Court dismissed the five counts of rape in the first degree and the three counts of…”

People v. Demagall, 63 A.D.3d 34 (N.Y. App. Div. 2009). · cites it 3× “15; Penal Law § 40.15). County Court, however, rejected the plea.”

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