Adolescent self-mutilative behavior (SMB) is a pervasive and dangerous problem, yet factors influencing the performance of SMB are not well understood. The authors examined the contextual features and behavioral functions of SMB in a sample of 89 adolescent psychiatric inpatients. SMB typically was performed impulsively, in the absence of physical pain, and without the use of alcohol or drugs. Moreover, analyses supported the construct validity of a functional model in which adolescents reported engaging in SMB for both automatic and social reinforcement. Considering the functions of SMB clarified the relations between SMB and other clinical constructs reported in previous studies such as suicide attempts, posttraumatic stress, and social concerns and has direct implications for the assessment and treatment of SMB.