PurposeWe aimed to investigate the associations of sleep disturbance and sleep time with behavioral problems and to assess whether endogenous melatonin was associated with sleep-related factors and behavioral problems. MethodsSubjects were 234 boys and 203 girls, aged 3–6 years, in a cross-sectional study in Japan in 2006. Information related to children's sleep disturbance, sleep time, and behavioral problems was obtained from parent-administered questionnaires. Children's behavioral problems were assessed by the Strengths and Difficulties Questionnaire. The 6-sulfatoxymelatonin levels in first-void morning urine were measured by radioimmunoassay. ResultsAfter multiple adjustments for covariates, children who often snore at night (P = .011), awake at night (P = .019), and looked tired in the daytime (P = .041) had a higher total difficulties score. Earlier time of waking (trend P = .021) and earlier time for bed (trend P = .014) were associated with a lower total difficulties score. Children with higher creatinine-corrected 6-sulfatoxymelatonin had lower total difficulties scores (trend P = .011). There were no associations between creatinine-corrected 6-sulfatoxymelatonin and sleep-related factors. ConclusionsSleep disturbance, later times of sleeping and waking up, and lower melatonin levels might be involved in the development of pediatric behavioral disorders.