OBJECTIVES: To examine the extent to which smoking, alcohol, physical activity and mental health problems in 15-16-year-olds are associated with receipt of medical benefits in young adulthood, after adjustment for confounders. DESIGN: Prospective population-based cohort survey linked to national registers. PARTICIPANTS: In the ‘Youth studies’ from the Norwegian Institute of Public Health, 15 966 10th graders in 6 Norwegian counties answered a health behaviour and mental health questionnaire; 88% were linked to National Insurance Administration Registers (FD-Trygd). OUTCOME MEASURE: Time to receipt of medical benefits, based on FD-Trygd. Follow-up was from age 18 years until participants were aged 22-26 years. METHOD: We performed Cox regression analyses to examine the extent to which variations in health behaviour and mental health problems during 10th grade were associated with receipt of medical benefits during follow-up. RESULTS: Daily smoking at age 15-16 years was associated with a significant increase in hazard of receiving health benefits at follow-up compared with not smoking for boys, HR (95% CI) 1.56 (1.23 to 1.98), and for girls 1.47 (1.12 to 1.93). Physical activity was associated with a decrease in hazard compared with inactivity from 23% to 53% in boys and from 21% to 59% in girls, while use of alcohol showed a mixed pattern. The hazard for benefits use rose with increasing levels of emotional symptoms, peer problems, conduct problems and hyperactivity-inattention problems (Strengths and Difficulties Questionnaire) at 15-16 years among both genders. CONCLUSIONS: Health behaviour and mental health problems in adolescence are independent risk factors for receipt of medical benefits in young adulthood.