Although the subject of 'ethnicity and HIV (human immunodeficiency virus)' has received some research interest, the interface between religion and HIV/AIDS (acquired immunodeficiency syndrome) remains largely unexplored. Islam is the world's second largest religion, and Muslims form Britain's largest religious minority group with numbers estimated at over 1.6 million (UK Census, 2001). In this paper, we seek to describe Muslim customs and practices that may represent risk factors for developing HIV/AIDS. We use the term 'risk' in its epidemiological sense, indicating activities that may increase or decrease the chances of contracting HIV infection. We consider issues such as polygamy, attitudes towards extra-marital relationships, homosexuality and the custom of male circumcision, all of which may have a bearing on the risk of acquiring HIV/AIDS. An appreciation of such factors is, we argue, crucial in order to develop and implement culturally competent and sensitive population-based risk reduction strategies.