Objective Limited data exist on non-suicidal self-injury (NSSI) and suicide attempts among psychiatric patients in Korea. In this study, we investigated the clinical characteristics of patients who engaged in NSSI and/or suicide attempts. Methods We performed a retrospective medical chart review of patients with NSSI and/or suicide attempts at the psychiatric department of a university medical center in Seoul between 2017 and 2019. According to their history, patients were allocated to one of three groups: NSSI only, suicide attempts only and NSSI and suicide attempts group. Groups were compared based on sociodemographic characteristics and psychological assessments. Results Overall, 80 patients with NSSI and/or suicide attempts were evaluated. Patients with NSSI and suicide attempts were more likely to be female than the other two groups. Patients with NSSI and suicide attempts were more likely to suffer from Cluster B personality disorder than the other groups. And patients with NSSI and suicide attempts scored significantly higher on novelty-seeking in TCI and RC8, RC9 in MMPI-2. Conclusion Patients with NSSI and/or suicide attempts were more likely to be female, younger, and showed higher levels of psychological disturbances. These findings highlight the importance of early detection and intervention for patients with NSSI.