This study examined characteristics and biopsychosocial predictors of nonsuicidal self-injury in a sample (N = 753) of youth in residential care admitted between 2005 and 2010. To model the data, the authors used t-tests, chi-square tests, and multiple logistic regressions stratified by gender. Results suggested that 12% of youth engaged in nonsuicidal self-injury during treatment. The authors identified no significant difference between the prevalence of nonsuicidal self-injury and demographic information. Results from multiple logistic regression analyses identified that aggression, prior self-harm, and age at placement significantly contributed to nonsuicidal self-injury during residential care. Boys with elevated levels of aggression and a history of prior self-harm and younger girls with elevated aggression were at increased risk of nonsuicidal self-injury during treatment. These findings suggest a 2-3 variable model for classifying youth as being at risk for engaging in nonsuicidal self-injury in residential treatment. Furthermore, prevalence estimates of nonsuicidal self-injury among adolescents in residential treatment are similar to rates obtained from nonclinical community samples. Implications, limitations, and future directions of these findings are discussed.