Background: Sex offences are overrepresented in the mentally handicapped, but information about the characteristics and offence behaviour of this group is limited.
Method: A retrospective case note survey was made of 47 male patients referred for antisocial sexual behaviour.
Results: Of 191 offences and/or incidents committed, 55.5% were heterosexual, 24% indecent exposure, 12.4% homosexual, 13.6% serious and 3.6% involved physical assault. Average age of the offenders was 23.9 years, with a mean IQ of 59.5, and there was a high prevalence of family psychopathology, psychiatric illness, minor physical disabilities, sexual experience, impaired relationship skills and sexual recidivism. Recidivists showed a low specificity for offence type and age and sex of victim. Categorical analysis differentiated a 'sex offences only' group from a 'sex plus other offences' group in the key areas of psychopathology, offence behaviour and outcome; this was supported by factor analysis.
Conclusion: The finding of two subgroups of mentally handicapped male sex offenders has important implications for prevention, assessment and treatment.