The discussion focuses on those adults who have been convicted of crime and come to be sentenced who sufficiently depart from the prevailing norms of mental balance and rational competence as to be 'mentally ill.' This condition may continue to affect their behavior and be relevant to present problems of determining the sentence to be imposed, apart from its modulation of their degree of guilt. Current legislation for sentencing the mentally ill contains specific provisions for increasing punishment (sexual psychopath laws and dangerous offender laws) and for decreasing punishment (legislatively defined mitigating circumstances). All recent sentencing statutes provide for judicial discretion in their application, and the mental illness of the convicted offender may be relevant to the exercise of that discretion. In sentencing the mentally ill offender, it is properly argued that this is a condition that reduces moral culpability, thus diminishing the sanction justly deserved for the crime. It is also properly argued that some mental illness may increase the dangerousness of an offender, warranting an increase or extension of punishment. The sentencing judge must determine whether a sentence is to be mitigated or aggravated because of the offender's mental illness. If the base expectancy rate for recidivism is shown by reliable evidence to be substantially higher than the base expectancy rate of another offender with an identical record and convicted of a similar crime (but who is not mentally ill), then the sentence should be on the high range for the crime at issue. Otherwise, the sentence should be in the low range. Footnotes and 25 references are listed.