Objective This study evaluated the association between mood and anxiety symptoms and suicidal attempt (SA) and/or non-suicidal self-injury (NSSI) in adolescents seeking mental health services. We also tested predictors of SA and NSSI.Methods We retrospectively reviewed the medical records of 220 adolescents who completed psychological assessment in clinical sample. Participants did the Adolescent General Behavior Inventory (A-GBI) and Children’s Depression Inventory (CDI). SA and NSSI were assessed retrospectively by interview. The caregiver of participants completed the Beck Depression Inventory (BDI) for themselves.Results 17% of total participants had a history of SA, and 24% experienced NSSI. Both SA and NSSI were more common in girls. The score of depressive subscale on A-GBI was higher in adolescents with SA than those without. The participants with NSSI showed higher scores on CDI and depressive subscale on A-GBI than those without. SA was associated with maternal BDI and history of NSSI; female sex, depressive subscale on A-GBI, and history of SA with NSSI.Conclusion Our study found that NSSI and SA are strongly associated in adolescents. Female sex and depressive symptoms of the adolescents were also significantly associated with NSSI in Korean adolescent. Findings are consistent with patterns in other countries.