Every day, doctors are faced with the dilemma of starting a postexposure prophylaxis (PEP) against HIV, HBV and HCV. A 28 days course of highly active antiretroviral therapy, chosen on the basis of the source's HIV resistance profile, should be initiated, as soon as possible, to reduce the likelihood of HIV transmission. Complete vaccination against HBV (3 doses) is associated with a 100% seroprotection in children and 95% in adults. There is no specific prophylaxis against HCV. Because of the complexity of these situations, we have edited local guidelines, which take into account not only international and Swiss recommendations, but also our experts' opinions. It is important to stress that PEP does not replace standard precautions.