Section 65 — Insanity and mental incapacity
English translation
Whoever commits an offence at a time when he is unable to appreciate right and wrong, or unable to control himself, because of a defective mind, mental disease, or mental infirmity, shall not be punished for that offence.
But if the doer still retains some ability to appreciate right and wrong, or still retains some ability to control himself, he shall be punished for that offence, but the Court may inflict a punishment less than that provided by law for such offence to any extent.
This English translation is provided for reference only and has not yet been firm-verified — always rely on the Thai original.
Firm annotation
Section 65 is the insanity provision in Book 1 on Criminal Liability. Paragraph one grants a full excuse where a defective mind, mental disease, or mental infirmity left the doer, at the time of the act, unable to appreciate right and wrong or to control himself; the result is no punishment, not acquittal of the act. Paragraph two addresses partial incapacity: where some capacity remained, the doer is punished but the court may go below the statutory minimum to any extent. The section turns on the doer's mental state at the moment of the offence, proven by evidence, typically medical, and it is distinct from Section 66, which deals separately with intoxication. Diminished-capacity findings under paragraph two are a common sentencing lever in serious cases.
Why this matters in practice
Section 65 is the route to either a full excuse from punishment or a reduced sentence for a mentally ill defendant, but everything depends on the mental state at the moment of the offence, not before or after. The burden of raising and supporting the defence falls on the accused, and courts require clear medical evidence that the doer could not appreciate right and wrong or control himself; the ability to communicate normally and a history of illness alone are often insufficient. In practice, partial incapacity under paragraph two is the more realistic outcome, yielding a below-minimum sentence. Securing a proper psychiatric assessment early, with legal guidance, is critical.
Supreme Court decisions interpreting this section
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Supreme Court Judgment No. 8699/2563 (2020)
To rely on partial mental incapacity under Section 65 paragraph two, there must be clear evidence that at the time of the offence the defendant could not, wholly or partly, appreciate right and wrong or control himself.
The defendant claimed mental impairment from cerebral and cardiac vascular disease under Section 65 paragraph two. The Court found the treating physician did not confirm any inability to appreciate right and wrong or to control himself, and that the defendant could communicate like a normal person, so the claim failed.
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Supreme Court Judgment No. 7791/2555 (2012)
Where a defendant had a defective mind at the time of the offence but still retained some ability to appreciate right and wrong and control himself, the court may impose a punishment below the statutory level under Section 65 paragraph two.
In a case of sexual offences against a child, the Court found that at the time of the offences the defendant had a defective mind but still retained some ability to appreciate right and wrong and control himself, and accordingly reduced the punishment below the statutory level under Section 65 paragraph two.
Curated decisions with case numbers verified against the Supreme Court database. English renderings are the firm's editorial translation for study.
Frequently asked questions
Does mental illness always mean no punishment?
No. Under Section 65, only where the illness left the person unable to appreciate right and wrong or to control himself at the time is there no punishment. If some capacity remained, he is punished, though the court may reduce the sentence below the statutory level.
What must be proved to rely on Section 65?
The defence must show, usually with medical evidence, the mental state at the moment of the offence, that a defective mind, mental disease, or mental infirmity made the person unable, wholly or partly, to appreciate right and wrong or to control himself.