Prior research consistently has shown a strong relation between childhood abuse and nonsuicidal self-injury (NSSI), yet it is unclear why this relation exists. The authors examined 2 specific posttraumatic stress disorder (PTSD) symptom clusters as potential mechanisms through which childhood abuse may be related to NSSI. Participants were 86 adolescents (78% female, 22% male; 73% Caucasian, 27% other races/ethnicities; mean age = 17.03 years, range = 12-19 years) who completed measures of childhood abuse, Diagnostic and Statistical Manual of Mental Disorders (4th ed.) PTSD symptoms, and NSSI. Analyses revealed a significant relation between childhood sexual abuse in particular and the presence and frequency of NSSI. Moreover, data supported a theoretical model in which PTSD reexperiencing and avoidance/numbing symptoms independently mediate this relation. Future research must test the temporal relation between childhood sexual abuse, PTSD symptoms, and NSSI and identify additional pathways to engagement in NSSI.