Homosexuality and bisexuality in sub-Saharan Africa, socially condemned and sometimes punishable under law, have rarely been the focus of scientific research. Senegal has been a pioneer in this area, with several sociological and epidemiological studies conducted in the early 2000s as part of the country’s effort to combat AIDS. In this paper, Joseph Larmarange, Annabel Desgrées du Loû, Catherine Enel and Abdoulaye Wade present the results of a new survey carried out in 2007 on 501 men aged 18 years and over, both married or single, but with experience of sexual relations with other men. Using a detailed description of the many types of bisexuality in Senegal, the authors identifed six major “modes of sexual activity” based on the characteristics of the respondents’ sexual partners during the preceding year and at the time of the survey. This typology demonstrates the diversity and complexity of behaviours in terms of age at first sexual intercourse, sex of the first partner, number of partners and type of sexual practice. The differences in HIV prevalence and exposure to violence between the various modes of sexual activity open up new scope for preventive action.