The collection of descriptive data on sex offenders has been marred by methodological problems: failing to distinguish between different types of sex offenders, or using selective samples form specialist institutions. The Challenge Project is a community project for perpetrators of child sexual abuse in South East London. Over a 2 year period, all convicted child molesters appearing before the court for sentencing or applying for parole were assessed by the Project Team. Data was collected on a range of personal, offense-related, and psychometric variables. Some of these were replicated on violent and property offender populations to allow for a preliminary comparison to be made. The descriptive profile of the offenders mirrored findings of previous research, and the comparison with other offender groups suggested that there is a cluster of childhood experiences which differentiate these sex offenders from other types of offenders. The research findings supported the hypothesis that perpetrators of child sexual abuse from a heterogeneous group of offenders, with identifiable--albeit overlapping--subgroups related to key variables such as a history of sexual abuse, repeat offending, and victim gender and relationship. The essential importance of these variables in relation to compliance with and response to treatment is discussed in further research.