Objective: To share the lessons learned when recruiting and retaining Peruvian female sex workers (FSWs) in a clinical trial. Methods: Peruvian FSWs 18-26 years of age were asked to join a clinical study of HPV vaccine starting in August 2009. Condoms, lubricants, and health services were given as an incentive to join the study, as well as a gift valued at three US dollars at each study visit for retention purposes. Results: 120 participants completed the survey. Barriers to non-enrollment recruiting included the false association of our clinical trial with an ineffective HIV vaccine study, plans to become pregnant during the vaccine study, not identifying as sex workers, pushback from husbands with fear of vaccine related birth defects, questioning motives for a free vaccine, not wanting to use birth control, lack of high perceived value of incentives, and limited time availability. Barriers to retention included periodic travel out of Lima, high costs for commuting, the requirement of no clients one day before the visit, and misinformation by health care providers regarding associations between the vaccine and illnesses. Conclusions: Working with health promoters and brothel managers, making periodic phone call reminders of appointments, and identifying participants who were peer leaders helped facilitate study participation and retention. Despite hardships in recruiting and retaining female sex workers, this group will participate in a study they deem useful for their health. Before recruiting female sex workers in clinical trials, potential barriers need to be addressed by study investigators.