Adolescent eveningness is associated with age, parental monitoring, daytime sleepiness, sleep problems, moodiness, and the use of coffee. This study investigated the association between adolescent morningness-eveningness and psychopathology, substance use, and suicidality in 1332 students ages 12 to 13. Each student-participant completed the Chinese version of the Child Morningness/Eveningness Scale (CMES), the Pubertal Development Scale, and a questionnaire about their sleep schedule, trouble sleeping, habitual substance use, and suicidality. Their mothers completed the Child Behavioral Checklist and Chinese Health Questionnaire. The morning (n = 412), intermediate (n = 740), and evening (n = 180) groups were operationally defined by the CMES t scores. The mixed model was used for data analysis. The evening group had shorter weekday sleep time, longer weekend sleep time, more daytime napping, and greater sleep compensation on weekends and was more likely than the other 2 groups to have behavioral/emotional problems, suicidality, and habitual substance use. Internalizing and externalizing problems partially explained the association between eveningness, substance use, and suicidality. The findings suggest that eveningness may be an indicator for adolescents with behavioral/emotional problems and risky behaviors and suggest an investigation for possible intervention.