34 Men who have sex with men (MSM) are at much greater risk of HIV infection in 35 Africa. Little is known about their involvement in transactional sex (TS). We 36 aimed to characterize MSM reporting TS (MSM-TS) and to identify factors 37 associated with their sexual practices using data from the prospective cohort study 38 CohMSM conducted in Burkina Faso, Côte d'Ivoire, Mali and Togo. Our study 39 focused on HIV-negative MSM, recruited between 06/2015 and 01/2018 by a 40 team of trained peer educators. Scheduled study visits at 6, 12 and 18 months 41 included medical examinations, HIV screening, risk-reduction counselling and 42 face-to-face interviews to collect information on their sociodemographic 43 characteristics, sexual behaviours, and HIV risk-reduction strategies. Three 44 stigmatization sub-scores were constructed. The generalized estimating equation 45 method was used for data analysis. Of the 630 HIV-negative participants recruited 46 at baseline, 463, 410 and 244 had a follow-up visit at 6-and 12-and 18-months, 47 respectively. Over a total of 1747 visits, 478 TS encounters were reported by 289 48 MSM-TS (45.9%). Of the latter, 91 participants reported systematic TS (31.5%), 49 55 (19.0 %) stopped reporting TS after baseline, and 53 (18.3%) reported TS after 50 baseline. Ninety participants (31.1 %) reported occasional TS. After adjusting for 51 country of study and follow-up visits, the following factors, reported for the 52 previous 6 months, were associated with a greater likelihood of TS: younger age, 53 an educational level