Past research has shown that 37% to 52% of sexual assault survivors report experiencing a set of peritraumatic responses, which include gross motor inhibition, analgesia, and fixed or unfocused staring. This response set closely resembles a set of unconditioned responses, collectively known as Tonic Immobility (TI). This study examined TI among childhood sexual abuse (CSA) survivors and its relation to PTSD symptomatology. Participants were 131 female college undergraduates who completed questionnaires assessing sexual abuse history, TI, and PTSD symptom severity. Results showed that TI partially mediated the relation between peritraumatic fear and overall PTSD symptom severity and completely mediated the relation between fear and the PTSD reexperiencing symptoms. Although peritraumatic fear is associated with TI, the mediation findings provide evidence for the notion that these responses are separate from one another. These results suggest that TI during CSA may play an important role in the subsequent PTSD symptomatology in adulthood. (Contains 3 tables, 1 figure, and 1 note.)