Young people presenting with sexually abusive behaviour (SAB) -juvenile sexual abusers (JSAs) -are responsible for a significant minority of sexual offences against children and adults (Home Office, 2003). A detailed study of 280 JSAs referred to a specialist Child and Adolescent Mental Health Service was conducted in order to provide a detailed description of this population. Data were obtained from a retrospective file review, and the Offenders Index. Two theoretical questions were addressed.Firstly, whether the age of onset of SAB could distinguish distinct subgroups of JSAs. Such categories have proved clinically relevant for generally anti-social juveniles (Moffitt, 1993). Early Onset (n=93) and Late Onset (n=120) groups were identified depending on whether SAB began before or after the age of 11. The results indicated that the Early Onset group were more likely to experience: inadequate family sexual boundaries; multiple forms of abuse; poorer parenting; and insecure attachment. The Late Onset group tended to misuse substances, sexually abuse specific groups, and were more likely to use verbal coercion.Secondly, whether a distinct subgroup of juvenile sexual abusers could be identified on the basis of emerging severe personality disorder (ESPD) traits. An ESPD group (n=54) presenting with marked conduct disorder and psychopathic personality disorder traits was compared with a non-ESPD group of JSAs (n=149). The results indicated that the ESPD group was more likely to have: an early difficult temperament; more insecure attachment; inconsistent parenting; placement disruption; and parents with mental health problems. Their SAB was more predatory and premeditated. Notably, their 'lifetime' conviction rate for all offences was 67 per cent compared to 37 per cent in the non-ESPD group.Clinical, policy and research implications are discussed. The need for JSA specialist services, integrated governmental approaches, and research on treatment efficacy, and ESPD traits in childhood are highlighted.