BackgroundTo estimate the prevalence and co-occurrence of health-related needs among young people aged 18 to 24 years transitioning out of adult prisons.MethodsData came from face-to-face, confidential interviews with adult prisoners aged 18–24 years in seven adult prisons in Queensland, Australia. We identified the prevalence and co-occurrence of overlapping health-related needs using an Australian health performance framework with four domains: physical health, mental health, risky substance use and socioeconomic disadvantage.ResultsMost young prisoners experience multiple and complex health problems prior to their release: 98% of young prisoners reported at least one indicator of poor health, and 30% reported at least one indicator of poor health in all four evaluated domains.ConclusionsYoung people in adult prisons report a high prevalence of health problems across multiple domains. Addressing these complex needs will require coordinated service delivery across health-related sectors both in custody and after release.