Objective: To determine the prevalence and types of deliberate self-harm (DSH) in adolescents, and associated factors. Design: A cross-sectional questionnaire study. Participants and setting: 3757 of 4097 Year 10 and Year 11 students (91.7%) from 14 high schools on the Gold Coast, Queensland, during September 2002. Main outcome measures: DSH behaviour, including descriptions of the last act, psychological symptoms, recent stressors, coping styles, help-seeking behaviour, lifestyle choices, and self-prescribing of medications. Results: 233 students (6.2%) met the criteria for DSH in the previous 12 months, with DSH more prevalent in females than males (OR, 7.5; 95% CI, 5.1-10.9). The main methods were self-cutting (138 respondents; 59.2%) and overdosing with medication (69 respondents; 29.6%). Factors associated with DSH included similar behaviours in friends or family, coping by self-blame, and self-prescribing of medications. Most self-harmers did not seek help before or after their most recent action, with those who did primarily consulting friends. Conclusions: DSH is common in Australian youth, especially in females. Preventive programs should encourage young people to consult health professionals in stressful situations.