Female sex workers are often considered highly vulnerable to sexually transmitted infections (STIs). However, data on STI epidemiology in female sex workers are lacking in Switzerland. Our main goal was to evaluate the prevalence of six STIs (human immunodeficiency virus [HIV], hepatitis B, hepatitis C, Chlamydia trachomatis, Neisseria gonorrhoeae and syphilis) among local female sex workers in Lausanne. A local, exploratory, cross-sectional study was conducted on a convenience sample of adult (≥18 years) Female sex workers in Lausanne, Switzerland, from 1 April 2015 to 31 December 2016. female sex workers who worked in street sex venues, massage parlours and brothels were approached for recruitment by a local non-governmental organisation. They were then invited to present at the Lausanne University Hospital, where they were offered a free STI screening and hepatitis A and B vaccination. We enrolled 96 female sex workers. They were predominantly undocumented immigrants (60%) from Africa and Eastern Europe with no health insurance; only one participant (1%) was Swiss born. During the study, 15 (16%; 95% confidence interval [CI] 9–23%) participants were newly confirmed to have an STI: six (6%; 95% CI 1–11%) had C. trachomatis, five (5%; 95% CI 0.6-9%) latent syphilis and four (4%; 95% CI 0.1–8%) hepatitis B (three with chronic active infection and one with past exposure). No human immunodeficiency virus (HIV) infections were newly diagnosed among the participants. Nineteen (20%) of the female sex workers were already vaccinated against hepatitis B, and 73 (76%) initiated vaccination against hepatitis A and hepatitis B during the study. Forty-four (46%) of the female sex workers required translation and assistance from social services.