Aim: Although health effects of social relationships are well-researched, long-term health consequences of adolescent family as well as peer relationships are poorly understood. The aim of the study was to explore the prospective importance of parental and peer social relationships in adolescence on internalising and functional somatic symptoms in adulthood. Methods: Data were drawn from four waves of the Northern Swedish Cohort Study, response rate 94.3%, N=1001. Outcome variables were internalising and functional somatic symptoms at the ages of 21, 30 and 42. Relationship variables at age 16 were poor parental contact and three indicators of poor peer relationships. Associations were assessed in multivariate ordinal logistic regressions with adjustment for confounders and baseline health. Results: Results show that the main relationships-related predictors of adult internalising symptoms were self-rated poor peer relationships in terms of spending time alone during after-school hours and poor parental relationship. Functional somatic symptoms on the other hand were most strongly associated with poor parental contact and not being happy with classmates at age 16. Conclusions: The quality of parental and peer relationships in adolescence predicts adult mental and functional somatic health as much as 26 years later, even when accounting for confounders and adolescent symptomatology. This study extends past research by exploring how both adolescent parental and peer relationships (self-reported as well as teacher reported) predict adult self-reported health.