Nelson Mandela has recently said that HIV/AIDS is the greatest health crisis in human history. At the end of 2001, UNAIDS estimated that there were 40 million people living with the infection, with 5 million new cases, and 3 million deaths per year. About half the infected individuals are men, and heterosexual intercourse is the commonest route of infection. Although condoms remain the first line of defence, they are unpopular in parts of Africa, where the pandemic is worst, so an alternative is needed. Post-coital penile hygiene has received little attention. Wiping the glans penis and inner foreskin immediately after intercourse with an acidic solution like lemon or lime juice, or even vinegar, should immediately kill the virus and might prevent infection; clinical trials are urgently needed. Several studies in Africa and India have now conclusively demonstrated a 2–7-fold protective effect of male circumcision against HIV infection. Circumcision removes the inner foreskin and the frenulum, which are the prime sites of HIV entry into the penis. Since male circumcision also protects men from human papilloma virus infection, and their wives from cervical carcinoma, the procedure should be encouraged in developed and developing countries.