A woman aged 36 injured herself on a needle that had been used to take an iliac-crest biopsy from an HIV-positive patient and a man aged 34 and a woman aged 35 had sexual contact with their HIV-positive partners during which the condom tore. They were given post-exposure prophylaxis (PEP) which was formulated using medication and virus resistance data from the HIV-positive individual. At 3 and 6 months the patients were all still HIV-negative. After occupational or non-occupational exposure to HIV, PEP is initiated if there is a reasonable risk of transmission of HIV. In The Netherlands a combination of 3 antiretroviral drugs is advised based on demonstrated antiviral effectiveness in the regular treatment of HIV-infections. Frequently a standard PEP-regimen is prescribed. If the source patient has a history of antiretroviral therapy, the virus might be resistant to standard PEP-regimens. In these cases the choice of drugs in the PEP-regimen can be individualised based on the antiretroviral medication history of the source patient and known resistance patterns of the source virus.