BackgroundPrecarious employment is a determinant of self-reported mental health problems among young adults. Less is known about more severe and objectively measured health outcomes, such as mental health problems requiring inpatient care. The current study aims to investigate the effect of precarious employment in early adulthood on later mental health problems requiring inpatient care. MethodA register-based cohort study, based on the Swedish Work, Illness and Labor-market Participation cohort, was conducted, following a cohort of young adults aged 27 years between 2000 and 2003 (born between 1973 and 1976) (n=339 403). Information on labour market position in early adulthood (precarious employment, substandard employment, unemployment and standard employment) was collected from registers 3 years after graduating from school. Information on the outcome of mental health problems (depression, anxiety and stress-related disorders) was collected from the National Patient Register. HRs with 95% CIs were obtained by Cox regression analyses. ResultsAfter adjusting for important covariates, such as prior mental health problems, compared with individuals in standard employment, individuals who were precariously employed in early adulthood had an increased risk of later mental health problems (HRadjusted: 1.51 95% CI 1.42 to 1.60). The association between precarious employment and mental health was slightly stronger for males. ConclusionsIn Sweden, entry into the labour market with precarious employment is associated with an increased risk of mental health problems, which is important given that precarious employment is becoming more prevalent among young adults.