PURPOSE: To describe medium-term physical and mental health and social outcomes following adolescent sexual assault, and examine users' perceived needs and experiences. METHOD: Longitudinal, mixed methods cohort study of adolescents aged 13-17 years recruited within 6 weeks of sexual assault (study entry) and followed to study end, 13-15 months post-assault. RESULTS: 75/141 participants were followed to study end (53% retention; 71 females) and 19 completed an in-depth qualitative interview. Despite many participants accessing support services, 54%, 59% and 72% remained at risk for depressive, anxiety and post-traumatic stress disorders 13-15 months post-assault. Physical symptoms were reported more frequently. Persistent (> 30 days) absence from school doubled between study entry and end, from 22 to 47%. Enduring mental ill-health and disengagement from education/employment were associated with psychosocial risk factors rather than assault characteristics. Qualitative data suggested inter-relationships between mental ill-health, physical health problems and disengagement from school, and poor understanding from schools regarding how to support young people post-assault. Baseline levels of smoking, alcohol and ever drug use were high and increased during the study period (only significantly for alcohol use). CONCLUSION: Adolescents presenting after sexual assault have high levels of vulnerability over a year post-assault. Many remain at risk for mental health disorders, highlighting the need for specialist intervention and ongoing support. A key concern for young people is disruption to their education. Multi-faceted support is needed to prevent social exclusion and further widening of health inequalities in this population, and to support young people in their immediate and long-term recovery.