Differences and similarities were studied in the functions of two different self-injurious behaviors (SIB): nonsuicidal self-injury (NSSI) and sex as self-injury (SASI). Based on type of SIB reported, adolescents were classified in one of three groups: NSSI only (n = 910), SASI only (n = 41), and both NSSI and SASI (n = 76). There was support for functional equivalence in the two forms of SIB, with automatic functions being most commonly endorsed in all three groups. There were also functional differences, with adolescents in the SASI only group reporting more social influence functions than those with NSSI only. Adolescents reporting both NSSI and SASI endorsed the highest number of functions for both behaviors. Clinical implications are discussed, emphasizing the need for emotion regulation skills.