BACKGROUND: One possible risk marker of later internalising symptoms is poor sleep, which is a problem for up to 40% of children. The present study investigated whether prior sleep problems could predict internalising symptoms over a period of 18 years of follow-up. METHODS: The study sample included 1503 French young adults from the TEMPO cohort (mean age=28.8±3.6 years) whose parents participate in the GAZEL cohort study. All TEMPO participants previously took part in a study of children's mental health and behaviour in 1991 (mean age=10.3±3.6 years) and 1999 (mean age=18.8±3.6 years). Sleep problems and internalising symptoms (depression, anxiety, somatic complaints) were assessed three times (1991, 1999, 2009) using the Achenbach System of Empirically Based Assessment (ASEBA) questionnaire. The association between sleep problems in 1991 and trajectories of internalising problems from 1991 to 2009 was tested in a multinomial logistic regression framework, controlling for sex, age, baseline temperament, behavioural problems and stressful life events, as well as family income, and parental history of depression. RESULTS: We identified four trajectories of internalising symptoms: high-persistent (2.5%), high-decreasing (11.4%), low-increasing (11.6%), and low-persistent (74.5%). After controlling for covariates, compared to participants who did not have sleep problems in 1991, those who did were 4.51 times (95% CI=1.54-13.19, P=.006) more likely to have high-persistent internalising symptoms and 3.69 times (95% CI=2.00-6.82, P<.001) more likely to have high-decreasing internalising symptoms over the 18-year follow-up. LIMITATIONS: Sleep problems and internalising symptoms were based on self-report questions, results should be interpreted with due caution. CONCLUSIONS: Sleep problems early in life are associated with an increased likelihood of internalising symptoms that persist from childhood to adulthood.