Background. This study investigated factors contributing to suspected offending behaviour by adults with a history of learning disabilities taken into custody at a city police station.

Methods. Adults charged with offences, and/or leaving custody, during a defined period, were identified as having a possible learning disability using a four-item questionnaire (Lyall et al. 1995a). A comparison group, of similar age, sex and IQ, was identified from a database of young people with learning difficulties. Information was obtained on interview about each individual's medical, psychiatric, social and family histories and psychological assessments were undertaken.

Results. In contrast to the comparison group, those in the ‘offending’ group were more likely to have a history of the following: losing contact with their father, forensic contact in one or more family members, past homelessness, illicit drug use, experiencing an excess of recent life events, self-reported behavioural problems at school, truancy, childhood police contact and contact with probation services. All had histories of repeated offending. There was also an increased rate of drug/alcohol dependence. Only two subjects in the study group had a full-scale IQ below 70.

Conclusions. These differences would suggest that the presence of childhood behavioural problems, offending behaviour by other family members, family separation and other social disruption and the development of drug and alcohol related problems are potentially the most important factors in trying to understand why one group engaged in criminal behaviour. The offending group had many characteristics in common with general offending populations.