Sampling methodology (e.g. population-based vs. clinical samples, anonymous self-reports vs. data collected as part of mandated treatment) affects the validity of conclusions drawn from research addressing the etiology of adolescent sexual offending. Studies of unselected samples allow testing of the generalizability of etiological models suggested from investigation of selected clinical or forensic populations. Further, representative epidemiological data on adolescent sexual offending is needed for policy-making and the planning of services. We conducted a national survey of all adolescent sexual offenders (ASOs, 12–17 years) referred to Social Services during 2000. Social workers at all child and adolescent units in Social Service authorities throughout Sweden (N=285, 99% response rate) completed a questionnaire about new ASO referrals in 2000. The National Board of Health and Welfare commissioned the survey and questionnaire items tapped offender, offence, and victim characteristics. A total of 197 boys and 2 girls aged 12–17 years were referred to Social Services because of sexually abusive behavior in 2000. Focusing specifically on males, this yielded a one-year incidence of .060% (95% confidence interval = .052–.068). Forty-six percent of male ASOs abused at least one child younger than age 12 years (child offenders) whereas the rest had abused peer or adult victims (peer offenders). Forty-two percent of male ASOs had ever committed sexual offences together with at least one other offender (group offenders). Child- vs. peer offenders and group vs. single offenders, suggested typologies in the literature, were compared to explore potential subtype-specific risk factors and correlates. The results suggested a higher proportion of group ASOs than previously reported and stronger support for subdividing ASOs into child vs. peer offenders than into group vs. single ASOs.