Background: Adolescent non-suicidal self-injurious behavior (NSSI) is a major public health concern. Although widespread, it is yet often a hidden problem. The purpose of this study was to explore the characteristics of self-injurious behavior in youth treated in an in-patient psychiatric unit. Subjects and methods: The study included 105 adolescents with a history of NSSI (mean age 15 years, 80% females) that underwent inpatient psychiatric treatment at a specialized facility. The factors assessed were sociodemographic data, frequency and type of NSSI, history of psychiatric disorder in family, existence of past traumatic event, alcohol, cigarettes and drug dependance and clinical psychiatric diagnosis. Retrospective-chart review study. Results: Of all assessed, patients with NSSI were predominantly female adolescents. Mean age onset of NSSI in the sample was 15 years. Equal number of patients showed occasional and repetitive NSSI, using self-cutting as a most common mean of self-injury. Approximately ¼ of adolescents met criteria for an adjustment disorder and ¼ for a mixed disorder of conduct and emotions. A low 7.8% met the criterion for borderline personality disorder. We found a statistically significant correlation between alcohol consumption and frequency of self-injurious behavior. Conclusions: Our study points to the fact that there has been an increase in prevalence of NSSI. Also, NSSI showed to be associated with female gender, alcohol consumption and a broad spectrum of comorbidities. Future research should focus not only on adolescents being hospitalized and treated, but should be representative of the whole young population because there are no national statistics on NSSI among young people in Croatia. Furthermore, future studies should focus on the origin of NSSI as opposed to its characteristics, in order for professionals to be able to prevent the issue.