We report the case of a woman who was found to be HIV positive after a sexual assault, in the absence of other risk factors for HIV infection. This observation and the report of one similar case support the view that HIV may be transmitted to a victim of a single sexual assault. We believe that all victims of rape should be offered a test for HIV and offered counselling. In addition to the current recommendations, the semen obtained should be tested for HIV antibodies by Western blot analysis. In the absence of clear data on safety and efficacy, we should recommend neither routine application of virucidal agents nor systematic Zidovudine (AZT) prophylaxis.