Wisconsin § 971.15 - Mental responsibility of defendant.
Full text of Wisconsin Wisconsin Statutes § 971.15 — Mental responsibility of defendant., with citation guidance and answers to common questions.
§ 971.15. Mental responsibility of defendant.
971.15(1) (1) A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect the person lacked substantial capacity either to appreciate the wrongfulness of his or her conduct or conform his or her conduct to the requirements of law. 971.15(2) (2) As used in this chapter, the terms “mental disease or defect” do not include an abnormality manifested only by repeated criminal or otherwise antisocial conduct. 971.15(3) (3) Mental disease or defect excluding responsibility is an affirmative defense which the defendant must establish to a reasonable certainty by the greater weight of the credible evidence. 971.15 History History: 1993 a. 486 . 971.15 Annotation It is not a violation of due process to put the burden of the affirmative defense of mental disease or defect on the defendant. State v. Hebard, 50 Wis. 2d 408 , 184 N.W.2d 156 (1971). 971.15 Annotation Psychomotor epilepsy may be legally classified as a mental disease or defect. Sprague v. State, 52 Wis. 2d 89 , 187 N.W.2d 784 (1971). 971.15 Annotation The state does not have to produce evidence contradicting an insanity defense. The burden is on the defendant. Gibson v. State, 55 Wis. 2d 110 , 197 N.W.2d 813 (1972). 971.15 Annotation A voluntarily drugged condition is not a form of insanity that can constitute a mental defect or disease. Medical testimony cannot be used both on the issue of guilt to prove lack of intent and also to prove insanity. Gibson v. State, 55 Wis. 2d 110 , 197 N.W.2d 813 (1972). 971.15 Annotation The legislature, in enacting the American Law Institute definition of insanity as this section, deliberately and positively excluded “antisocial conduct” from the statutory definition of “mental disease or defect.” Simpson v. State, 62 Wis. 2d 605 , 215 N.W.2d 435 (1974). 971.15 Annotation The jury was not obliged to accept the testimony of two medical witnesses, although the state did not present medical testimony, because it was the jury’s responsibility to determine the weight and credibility of the medical testimony. Pautz v. State, 64 Wis. 2d 469 , 219 N.W.2d 327 (1974). 971.15 Annotation The court properly directed the verdict against the defendant on the issue of mental disease or defect. State v. Leach, 124 Wis. 2d 648 , 370 N.W.2d 240 (1985). 971.15 Annotation Discussing use of expert evidence of personality dysfunction in the guilt phase of a criminal trial. State v. Morgan, 195 Wis. 2d 388 , 536 N.W.2d 425 (Ct. App. 1995), 93-2611 . 971.15 Annotation When a defendant requests an 11th-hour change to a not guilty by reason of mental disease or defect plea, the defendant has the burden of showing why the change is appropriate. There must be an offer of proof encompassing the elements of the defense and a showing of why the plea was not entered earlier. State v. Oswald, 2000 WI App 3 , 232 Wis. 2d 103 , 606 N.W.2d 238 , 97-1219 . 971.15 Annotation A court is not required to conduct an on-the-record colloquy with respect to a defendant’s desire to abandon a not guilty by reason of mental disease or defect plea. Only fundamental constitutional rights warrant this special protection, and such a plea falls outside the realm of fundamental rights. State v. Francis, 2005 WI App 161 , 285 Wis. 2d 451 , 701 N.W.2d 632 , 04-1360 . 971.15 Annotation A court is not required to inform a defendant during a plea colloquy that the defendant may plead guilty to a crime and still have a jury trial on the issue of mental responsibility. Because neither the federal or state constitutions confers a right to an insanity defense, a court has no obligation to personally address a defendant in regard to the withdrawal of a not guilty by reason of mental disease or defect plea, although it is the better practice to do so. State v. Burton, 2013 WI 61 , 349 Wis. 2d 1 , 832 N.W.2d 611 , 11-0450 . 971.15 Annotation Although expert testimony may be helpful to a defendant in the responsibility phase of the trial, a favorable expert opinion is not an indispensable prerequisite to a finding of mental disease or defect. Although expert testimony is not required, it is highly unlikely that a defendant’s own testimony, standing alone, will be sufficient to satisfy the burden of proof. State v. Magett, 2014 WI 67 , 355 Wis. 2d 617 , 850 N.W.2d 42 , 10-1639 . 971.15 Annotation Because every person is competent to be a witness under s. 906.01 and there is no exception in s. 906.01 for defendants who have entered a plea of not guilty by reason of mental disease or defect, a defendant is competent to testify to the defendant’s own mental health at the responsibility phase of a trial. This does not mean, however, that the defendant’s testimony alone is sufficient to raise a question for the jury. State v. Magett, 2014 WI 67 , 355 Wis. 2d 617 , 850 N.W.2d 42 , 10-1639 . 971.15 Annotation Consumption of prescription medication cannot give rise to a mental defect that would sustain an insanity defense. Furthermore, it is established law that one who mixes prescription medication with alcohol is responsible for any resulting mental state. State v. Anderson, 2014 WI 93 , 357 Wis. 2d 337 , 851 N.W.2d 760 , 11-1467 . 971.15 Annotation Although a better practice, a circuit court is not required to conduct a right-to-testify colloquy at the responsibility phase of a bifurcated trial resulting from a plea of not guilty by reason of mental disease or defect. State v. Lagrone, 2016 WI 26 , 368 Wis. 2d 1 , 878 N.W.2d 636 , 13-1424 . 971.15 Annotation The Power of the Psychiatric Excuse. Halleck. 53 MLR 229 (1970). 971.15 Annotation The Insanity Defense: Conceptual Confusion and the Erosion of Fairness. MacBain. 67 MLR 1 (1983). 971.15 Annotation Criminal Law—First Degree Murder—Evidence of Diminished Capacity Inadmissible to Show Lack of Intent. Gertig. 1976 WLR 623.
Source: official Wisconsin text · Last verified 2026-08-27
Frequently Asked Questions About Wisconsin § 971.15
What does Wisconsin Statutes § 971.15 cover?
Section 971.15 ("Mental responsibility of defendant.") is part of the Wisconsin Statutes, the codified statutory law of Wisconsin. It sets out the legal rule or procedure described in the text above. Statutes are amended regularly, so always verify against the official source.
How do I cite Wisconsin § 971.15?
A common citation format is "Wisconsin Statutes § 971.15" (Wisconsin). Legal writing may require the code abbreviation, section number, and year or edition. Match the style required by your court, professor, or publisher.
Is this the official text of Wisconsin law?
No. This page is for research and education and may not include the most recent amendments. For official current law, check the Wisconsin official source linked on this page or consult a licensed Wisconsin attorney.
How does Wisconsin § 971.15 apply to my situation?
Statutes are interpreted in context, and application depends on your specific facts. Only a licensed attorney in Wisconsin can advise on how this section applies to you. Contact your state or local bar association for a referral.
Sources & Verification
Not legal advice. Verify against the official source and consult a licensed attorney in Wisconsin.