Crimes Act 1961

Matters of justification or excuse - Insanity

23: Insanity

You could also call this:

"What happens if you're not in control of your mind when you break the law?"

When you do something or don't do something, the law assumes you are sane. You are considered sane until it is proven that you are not. The law says this to make sure you are treated fairly.

If you have a disease of the mind or are not very intelligent, you might not be able to understand what you are doing. You might not know if what you are doing is right or wrong, based on what most people think is right or wrong. In this case, you might not be guilty of a crime.

If you were insane before or after you did something, or if you had insane thoughts, this can be used as evidence to show you were not responsible for your actions. This means you might not be guilty of a crime if you were not in control of your mind. The law looks at your state of mind when you did something to decide if you are guilty.

If you are not guilty of a crime because of your state of mind, this does not affect whether someone else who was involved in the crime is guilty. The law treats each person separately, so if someone else was involved in the crime, they can still be found guilty even if you are not. This ensures that everyone is held responsible for their actions.

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This page was last updated on 4 August 2025

View the original legislation for this page at https://legislation.govt.nz/act/public/1986/0120/latest/link.aspx?id=DLM328219.

Topics:

Crime and justice > Criminal law

22: Children between 10 and 14, or

"Children aged 10-14 are only guilty of a crime if they knew what they did was wrong."

24: Compulsion, or

"Doing something wrong because someone is forcing you to, might not get you in trouble with the law."

Part 3Matters of justification or excuse
Insanity

23Insanity

Every one shall be presumed to be sane at the time of doing or omitting any act until the contrary is proved.
No person shall be convicted of an offence by reason of an act done or omitted by him or her when labouring under natural imbecility or disease of the mind to such an extent as to render him or her incapable—
of understanding the nature and quality of the act or omission; or
of knowing that the act or omission was morally wrong, having regard to the commonly accepted standards of right and wrong.

Insanity before or after the time when he or she did or omitted the act, and insane delusions, though only partial, may be evidence that the offender was, at the time when he or she did or omitted the act, in such a condition of mind as to render him or her irresponsible for the act or omission.
The fact that by virtue of this section any person has not been or is not liable to be convicted of an offence shall not affect the question whether any other person who is alleged to be a party to that offence is guilty of that offence.

Compare

1908 No 32 s 43