The prevalence of personality disorders has been determined by studies of both the general population and mental handicap hospitals. The present study attempts to determine the prevalence of personality disorders in a community sample and to check the implications for treatment. A community sample of learning disability service users was surveyed by obtaining a rating from a good informant to establish demographic data, level of functioning and the nature of personality disorders, if any, using the ICD-10 version of the Standardized Assessment of Personality (SAP). Fifty per cent of the sample had personality abnormalities, and 31% had sufficient impairment of the social and occupational domains and personal distress to warrant a diagnosis of personality disorder. These findings are compared with previous studies. Paranoid, schizoid, impulsive and dissocial personality abnormalities were seen to be associated with a high referral rate to psychiatric services and needed considerable therapeutic input. The prevalence of personality abnormalities in community populations with a learning disability is high. The SAP is a useful instrument for screening. This subpopulation makes significant demands on community psychiatric services.