Senegal is the only African country where sex work is legal and regulated by a health policy. Senegalese female sex workers (FSWs) are required to register with a health facility and to attend monthly routine health checks aimed at testing and treating sexually transmitted infections (STIs). Compliance to those routine visits is recorded on a registration card that must be carried by FSWs in order to avoid sanctions in case of police arrests. Although this policy was first introduced in 1969 to limit the spread of STIs, there is no evidence so far of its impact on FSWs' health and well-being. The paper aims to fill this gap by exploiting a unique data set of registered and unregistered Senegalese FSWs. Using propensity score matching, we find that registration has a positive effect on FSWs' health. However, we find that registration reduces FSWs' subjective well-being. This finding is explained by the fact that registered FSWs are found to engage in more sex acts, in riskier sex acts, have less social support from their peers, and are more likely to experience violence from clients and police officers. We prove that those results are robust to the violation of the conditional independence assumption, to misspecification of the propensity score model, and that covariate balance is achieved. The results suggest that more efforts should be deployed to reduce the stigma associated with registration and to address the poor well-being of FSWs, which is counterproductive to HIV prevention efforts.