The purpose of the study was to examine the quantitative risk of criminal behavior associated with specific mental disorders. Method: An unselected 1966 birth cohort (N=12,058) in Northern Finland was prospectively studied until the end of 1992. The investigation started during the mothers' pregnancy, and the data on the subjects' family characteristics, mental and physical development, living habits, psychiatric morbidity, and criminal records were gathered at various times. Results: The prevalence of offenses was the highest among males with alcohol-induced psychoses and male schizophrenic subjects with coexisting alcohol abuse, and more than half of the schizophrenic offenders also had problems with alcohol. Eleven (7%) of the 165 subjects who committed violent crimes were diagnosed as psychotic. Male schizophrenic subjects had a moderately high risk for violent offenses, but the risk for other types of crimes was not elevated significantly. Odds ratios for criminal behavior were adjusted according to the socioeconomic status of the childhood family and were the same as or slightly lower than the crude odds ratios for all disorders except schizophrenia and mood disorders with psychotic features. Conclusions: The results indicate that the risk of criminal behavior was significantly higher among subjects with psychotic disorders, even though the socioeconomic status of the childhood family was controlled. The higher risk for violent behavior was associated especially with alcohol-induced psychoses and with schizophrenia with coexisting substance abuse. The results suggest that schizophrenia without substance abuse may also be associated with a higher risk of offenses, but this finding is tentative and requires further investigation.