Using results from a large Norwegian follow-up study of former adolescent psychiatric in-patients we have traced the progression from mental disorders requiring hospitalisation in adolescence to registered criminal behaviour in adulthood, particularly highlighting gender differences. A nationwide representative sample of 1095 adolescent psychiatric inpatients (46% females) was followed up 15-33 years after admission to the National Centre for Child and Adolescent Psychiatry in Oslo, Norway. In adolescence 45% fulfilled the DSM-IV criteria for a disruptive behaviour disorder. At follow-up, 63% of the males and 39% of the females had a criminal record. Among females, psychoactive substance use disorder in adolescence seemed to be a sine qua non for later registered criminality, with intravenous drug use a potent risk factor for life-course-persistent criminality. The same strong association between drug use and criminality was not found in males. Factor analysis demonstrated that while the DSM-IV Conduct Disorder criteria structure was similar across genders, the prevalence of the various forms of expression was different in males and females. The differences between individuals with violent and non-violent crimes were more substantial in males than in females. There were marked gender differences in the criminal profiles observed, with the females' criminal career developing in a less serious manner than in males: females had later criminal debut, a lower number of acts on record, less diverse criminal behaviour, and an escalation in the severity of offences over time was less frequently encountered. However, secular trend analyses indicated that gender differences had diminished over the last several decades, with females "catching up" with their male counterparts. Overall, the results demonstrated important qualitative and quantitative gender differences in the criminal behaviour of former adolescent psychiatric in-patients. The results may be of use in prevention.