Although illegal in Egypt, prostitution exists. The prevalence of HIV infection among female sex workers (FSWs) in Cairo is not precisely known. This cross-sectional study investigated the high-risk behaviour for HIV infection and HIV prevalence among FSWs in greater Cairo. A total of 431 FSWs were interviewed about their sexual history with paid and unpaid partners, condom use and risky behaviour for HIV infection; all were tested for HIV. Use of alcohol and drugs was reported by 39.9% and 49.0% of the women respectively; 37.6% only used such substances while with a client. Male condoms were known by 72.6% but their use in the previous month was low (32.8%) and only 22.4% had used one with their last client. The main reasons for not using condoms were not thinking of it (40.6%) and client refusal (20.5%). All the women tested negative for HIV infection. The high-risk behaviour of many FSWs necessitates intervention programmes to reduce their risk of HIV infection.