Last week the United States Department of Health and Human Services published updated recommendations for the use of post-exposure prophylaxis (PEP) following non-occupational exposure to HIV. The evidence is still unclear as to the efficacy of this intervention and this report provides a comprehensive overview of available literature, and discusses the benefits and problems with the administration of PEP in certain circumstances. It also clearly re-emphasises that the most effective way to prevent transmission of HIV is to prevent exposure, and any programme of PEP administration should not replace primary prevention.