This systematic review of 52 studies (2005-2011) examines the prevalence of non-suicidal self-injury (NSSI) and deliberate self-harm (DSH) among adolescents globally. The results show no statistically significant difference between NSSI (18.0% SD = 7.3) and DSH (16.1% SD = 11.6) prevalence rates. Single-item questions led to lower prevalence estimates compared to behavior checklists. Mean prevalence rates have not increased in the past five years, suggesting stabilization. The study highlights the need for a common assessment approach to facilitate cross-cultural comparisons. NSSI and DSH have comparable prevalence across countries, but differences in assessment methods and definitions contribute to variability in estimates. The study also found that prevalence estimates vary depending on the time frame assessed (lifetime vs. 12-month) and the type of assessment tool used (behavioral checklist vs. single-item). Overall, the data suggest that the global prevalence of self-injury among adolescents has stabilized in recent years. The study emphasizes the importance of using consistent assessment methods to improve understanding of self-injury and its cultural validity. The findings support the DSM-5 proposal for a non-suicidal self-injury disorder but highlight the need for further research to ensure cultural validity and accuracy in diagnosis.This systematic review of 52 studies (2005-2011) examines the prevalence of non-suicidal self-injury (NSSI) and deliberate self-harm (DSH) among adolescents globally. The results show no statistically significant difference between NSSI (18.0% SD = 7.3) and DSH (16.1% SD = 11.6) prevalence rates. Single-item questions led to lower prevalence estimates compared to behavior checklists. Mean prevalence rates have not increased in the past five years, suggesting stabilization. The study highlights the need for a common assessment approach to facilitate cross-cultural comparisons. NSSI and DSH have comparable prevalence across countries, but differences in assessment methods and definitions contribute to variability in estimates. The study also found that prevalence estimates vary depending on the time frame assessed (lifetime vs. 12-month) and the type of assessment tool used (behavioral checklist vs. single-item). Overall, the data suggest that the global prevalence of self-injury among adolescents has stabilized in recent years. The study emphasizes the importance of using consistent assessment methods to improve understanding of self-injury and its cultural validity. The findings support the DSM-5 proposal for a non-suicidal self-injury disorder but highlight the need for further research to ensure cultural validity and accuracy in diagnosis.