Mycoplasma genitalium is associated with cervicitis and pelvic inflammatory disease but little is known about its role in pregnancy. We investigated the prevalence of M. genitalium by polymerase chain reaction assay on urine specimens from 1216 pregnant women (mean age 31years) presenting before 10 weeks of gestation in 32 general practices. The prevalence of M. genitalium was 0.7% (6/915, 95% CI 0.1–1.2). It was more common in women aged <20 years, women of Afro-Caribbean or black African ethnic origin, women in social classes 3–5 and single women. Only one woman with M. genitalium infection miscarried, and none of those followed up to term had a preterm birth, although the numbers were small. The low prevalence of M. genitalium infection suggests it is unlikely to be an important risk factor in adverse pregnancy outcome in healthy women in the community.