Active resistance is considered to be the "normal" reaction during rape. However, studies have indicated that similar to animals, humans exposed to extreme threat may react with a state of involuntary, temporary motor inhibition known as tonic immobility. The aim of the present study was to assess the occurrence of tonic immobility during rape and subsequent posttraumatic stress disorder and severe depression MATERIAL AND METHODS: Tonic immobility at the time of the assault was assessed using the Tonic Immobility Scale in 298 women who had visited the Emergency clinic for raped women within 1 month of a sexual assault. Information about the assault and the victim characteristics were taken from the structured clinical data files. After 6 months, 189 women were assessed regarding the development of posttraumatic stress disorder and depression RESULTS: Of the 298 women, 70% reported significant tonic immobility and 48% reported extreme tonic immobility during the assault. Tonic immobility was associated with the development of posttraumatic stress disorder (OR 2.75; 1.50-5.03, p = .001) and severe depression (OR 3.42; 1.51-7.72, p = .003) at 6 months. Further, prior trauma history (OR 2.36; 1.48-3.77, p <.001) and psychiatric treatment history (OR 2.00; 1.26-3.19, p = .003) were associated with the TI response CONCLUSIONS: Tonic immobility during rape is a common reaction associated with subsequent posttraumatic stress disorder and severe depression. Knowledge of this reaction in sexual assault victims is important in legal matters and for health care follow-up. This article is protected by copyright. All rights reserved.