Background: Chronic pain and fatigue are both common complaints in childhood and adolescence and often persist over time. The aim of the study was to investigate whether chronic pain/fatigue persists during adulthood and how former patients function and participate in society as adults. Methods: This historical cohort study used questionnaires to gather the data. Predictors for social participation in adulthood were also identified. Differences in functioning and health care use between young adults with current pain/fatigue complaints and those without were also discussed. Results: Ninety-four young adults responded; their mean age was 26.6 years and 91.5% were women. The average time since treatment was 10.2 years. 63.4% reported ongoing or new pain/fatigue complaints. 72.0% had a paid job; of those who worked, 22.1% reported taking sick leave in the past month. 78.7% of them reported having one or more chronic diseases. A higher level of pain/fatigue measured pre-treatment was identified as a predictor for more impaired social participation in adulthood. Young adults with current pain/fatigue complaints reported more healthcare utilization, lower levels of physical functioning and limitations in daily activities due to physical problems. Conclusions: A considerable number of these young adults still have pain/fatigue complaints in adulthood. More pain/fatigue pre-treatment during adolescence predict impaired functioning in the work-educational domain in young adulthood. What does this study add?: This study examines the social participation of young adults who suffered from severe chronic pain/fatigue during adolescence. Predictors for social participation are reported, as are the differences between young adults with and without persistent pain/fatigue complaints.