Background The intention of becoming pregnant has an evident impact on the prenatal and postnatal period. For female sex workers (FSWs) in West Africa, among whom pregnancies are frequent as are HIV and sexually transmitted infections, a better understanding of their pregnancy intention and its infuence on pregnancy occurrence could help prevent unwanted pregnancies and adverse efects on wanted pregnancies.Methods We recruited 330 FSWs in Benin and 322 in Mali and followed them for 12 months. We evaluated their pregnancy intention at recruitment and 6-month follow-up, using a multidimensional prospective measure that we developed. We assessed pregnancy occurrence with a pregnancy test and a retrospective questionnaire at 6 and 12 months. A Cox proportional hazard model was used to estimate the association between intention and preg‑nancy. We carried out an analysis to take losses to follow-up into account using the inverse of probability of censoring weights and a cluster analysis to corroborate that the multidimensional measure of pregnancy intention ftted the data. Results 407 FSWs were included in the frst 6-month analysis and 284 at 12 months. Mean age was 30.9 years. The pregnancy intention distribution was similar between the two periods: 15.2% in the frst period and 16.3% in the second had a positive intention. One out of four were ambivalent and almost 60% (57.7% and 56.3%) had a negative intention. For 38.2% of the FSWs, the intention changed between the two periods. The global incidence rate (to frst event) was 19.1 pregnancies per 100 person-years. There was a borderline signifcant trend (p=0.0529) of decreased pregnancy incidence with decreasing intention. Compared to positive intention, the adjusted hazard ratio (aHR) for ambivalent and negative intentions were 0.71 [95% confdence interval (95% CI) 0.32–1.60] and 0.46 (95% CI 0.21–1.01), respectively. Conclusion The level of pregnancy intention infuences its occurrence among FSWs and nearly one out of six wants a baby despite working in the sex trade. Programmatically, early identifcation of these women could facilitate provi‑sion of quality antenatal and postnatal care. Given other health risks associated with sex work this care may decrease potential risks of adverse maternal, fetal and neonatal outcomes