Background Men who have sex with other men (MSM) are in Africa a vulnerable population which has hitherto been insufficiently explored. Given the high rate of bisexuality among MSM, it is important to understand their risk-taking behaviours regarding both men and women. Methods A socio-behavioural survey was carried out in 2007 among 501 MSM recruited using the snowball sampling method. We explore in this article why a condom was not used during last sexual intercourse with a man and with a woman, bearing in mind the respondent’s characteristics, type of relationship and the context of the sexual act. Results 489 men reported that they had had sexual intercourse at least once with another man during the previous year, and 358 with a man and with a woman. With another man, the main risk factors are sexual intercourse in a public place (adjusted OR = 6.8), and non-participation in an MSM prevention program (adjusted OR = 3.1). The risks, although non-significant at 5%, are higher among younger men (18-19 years) and older men (35 years and over), and among vulnerable people (unemployed). With a woman, sexual intercourse with the respondent’s wife is hardly ever protected (2%). Otherwise, risks are high when the female partner is very young (15 years or younger, adjusted OR = 5.3) and when the man has not participated in an MSM prevention campaign (adjusted OR = 2.3). Conclusion Having participated in a prevention program specifically targeting MSM constitutes a major prevention factor. However, these programs targeting MSM must address their heterosexual practices and the specific risks involved.