Objective: We analysed the results of a 6 year screening period for Chlamydia trachomatis in a group of female sex workers (FSW) of all ages in Ghent, Belgium. Methods: They were tested in the context of an outreach health programme for sex workers. C trachomatis was tested by Cobas Amplicor CT/NG PCR. Results: In the 6 year period, 1643 tests were performed on 950 different sex workers (nationality: Belgian 60.3%, other western European (mostly French) 21.0%, African 12.4%, eastern European 3.0%, other 3.3%; workplace: bar/sauna 49.0%, private homes 31.8%, windows 18.2%, and escorts 1.0%). Baseline prevalence (only considering results of first test) was 70/950 or 7.4% (95% CI 5.7 to 9.0). The incidence rate was 98 episodes in 1347 person years or 7.3/100 person years (95% CI 5.9 to 8.7). There was a strong age effect. There was no clear relation with nationality or the workplace. Conclusions: The prevalence was higher than in general populations selected in Belgium, Britain, and the Netherlands. Since younger age is a risk factor for C trachomatis , it is very important to contact these women as soon as possible when they enter the trade. General screening for C trachomatis in young women is not common practice in Belgium. Sex workers often do not tell doctors about their work and will therefore not be screened unless in the context of specific outreach projects.