The aim of the present study was to examine differences in psychological symptoms and sense of self-competence between adolescents with and without non-suicidal self-injurious behavior. We collected data in a sample of 281 Flemish adolescents. Psychological symptoms and self-competencies were assessed by means of the Youth Self-Report (YSR) and NSSI was assessed using the Self-Harm Inventory (SHI-22). Results showed significant differences between adolescents with and without NSSI on all psychopathological subscales. Furthermore, adolescents engaging in NSSI reported significantly lower scores on social competence, but equal levels on other competencies. Results revealed that externalizing problems and attention/thought/social problems are significantly associated with NSSI. Results also showed that having a higher score on aggressive behavior or thought problems increases the chance of belonging to the NSSI group; whereas a higher score on the social competence scale decreases the chance of belonging to the NSSI group. Clinical implications of these findings are discussed. (Contains 5 tables.)