Many cases of mucopurulent cervicitis (MPC) are idiopathic and cannot be attributed to the known cervical pathogens Neisseria gonorrhoeae, Chlamydia trachomatis, or herpes simplex virus. Because Mycoplasma genitalium is associated with nongonoccocal urethritis in men, its role in MPC, the corresponding syndrome in women, was investigated. Archived cervical specimens from women recruited in the Harborview Sexually Transmitted Disease Clinic in Seattle from 1984 to 1986 were tested, using polymerase chain reaction, in a study that identified other causes of and risk factors for MPC. M. genitalium was detected in 50 (7.0%) of 719 women. Young age, multiple recent partners, prior miscarriage, smoking, menstrual cycle, and douching were positively associated with M. genitalium, whereas bacterial vaginosis and cunnilingus were negatively associated. After adjustment for age, phase of menstrual cycle, and presence of known cervical pathogens, women with M. genitalium had a 3.3-fold greater risk (95% confidence interval, 1.7-6.4) of MPC, which suggests that this organism may be a cause of MPC.