BackgroundMental health represents an important public health issue, and mental health problems have been linked to school dropout. This study aimed to identify mental health groups of high school students using both positive and negative aspects of mental health and to examine whether these mental health groups longitudinally predict school dropout.MethodsWe conducted latent class analysis using the Danish National Youth Study 2014 (n = 60,526; mean 17.9 years) to identify clustering of mental health (11 items covering positive and negative aspects of emotional wellbeing and functioning in daily life), separately by sex. The relationship with subsequent school dropout was examined using logistic regression models, adjusted for age, ethnicity and socioeconomic status. Information on dropout status was obtained through educational registers.ResultsSchool dropout rates was highest among first-year students. Four mental health groups were identified: Flourishing (females: 38%, males: 55%), moderate mental health (females: 15%, males: 20%), emotionally challenged (females: 28%, males: 15%) and languishing (females: 19%, males: 10%). Compared to the flourishing group, adjusted odds ratio (AOR) for dropout were 3.43 (95% CI: 2.98, 3.95), 1.73 (95% CI: 1.45, 2.06) and 1.76 (95% CI: 1.52, 2.04) in the languishing, moderate mentally healthy and emotional challenged females. Results in males were comparable.ConclusionsMental health in high school students cluster together in four categories among both males and females. Students who are languishing, emotionally challenged or moderate mentally healthy have about 1.5-fold to threefold higher risk of dropping out of high school compared with flourishing students. Universal mental health interventions may be a promising strategy, particularly in the first year of high school where most students drop out of school.