The present study investigated the prevalence of non-suicidal self-injury (NSSI) and suicidal self-injury (SSI) in a sample of 1,417 Flemish adolescents aged 12 to 18, as well as psychosocial differences between adolescents engaging in NSSI and adolescents engaging in SSI. Participants completed an anonymous online survey inquiring about NSSI and SSI functions, sociodemographic correlates, help seeking behaviors, and stressful life events. Lifetime prevalence of NSSI was 13.71% and SSI was 3.93%. No gender or age differences appeared between adolescents engaging in NSSI or SSI; however, differences in educational level were observed. Significant differences in functions of the behavior and number of stressful life events were noted between groups. Finally, the likelihood of receiving professional help differed between adolescents engaging in NSSI and adolescents engaging in SSI. Implications of the findings for assessment and treating NSSI and SSI are discussed.