OBJECTIVES: To identify the contribution of Mycoplasma genitalium to the aetiology of cervicitis in sub-Saharan Africa and its relative importance in the overall burden of sexually transmitted infections among female sex workers (FSW). METHODS: The study population consisted of FSW recruited in Ghana and Benin during the initial visit of a randomised controlled trial. A questionnaire was administered, a pelvic examination carried out, and cervical samples obtained for detection of M genitalium, Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis. Clinical signs potentially indicating cervicitis were cervical discharge, pus on the cervical swab, bleeding after sampling, and inflammatory cervix. RESULTS: Among 826 FSW, 26.3% were infected with M genitalium. N gonorrhoeae was strongly and independently associated with each of the four signs of cervicitis (adjusted odds ratios (AOR): 4.1 to 6.0). The AOR for C trachomatis were intermediate (1.3-4.1) and the AOR for M genitalium were lower (between 1.6 and 1.8) but statistically significant (p< or =0.05) for each sign. CONCLUSIONS: M genitalium is weakly associated with signs of cervicitis in west African FSW but is highly prevalent.