Characteristics of adolescents who sexually offend, their patterns of their offending behaviour and the defining features of their victims are firmly established in the overseas literature. The research literature in Australia, however, is less developed. This study describes the characteristics of a sample of clients of the Sex Offender Program of the New South Wales Department of Juvenile Justice and examines patterns of offence behaviours and related descriptions of victims. Adolescents who sexually offend in NSW have backgrounds of low educational attainment and abuse and a range of other social risk factors, and they are most likely to victimise female children. A typology of adolescent sex offenders based on their offending behaviour is offered.