The role of mucopurulent cervicitis in identifying pregnant women with Chlamydia trachomatis infection and poor pregnancy outcome was examined at the Johns Hopkins Hospital Obstetric Clinic in Baltimore, Maryland. The women studied were at high risk for chlamydial infection (14%), low birthweight (12%), and preterm delivery (13%). Yellow endocervical discharge on a cotton swab had a sensitivity of 23.9%, specificity of 89.4%, and positive predictive value of 28.6% for predicting chlamydial infection. The presence of greater than or equal to 30 polymorphonuclear cells per 1000 x field had a sensitivity of 25.0%, specificity of 87.6% and positive predictive value of 24.3%. Women with cervicitis defined by greater than or equal to 30 polymorphonuclear cells per 1000 x field were twice as likely to deliver a low-birthweight infant. Adjustment for potential confounding variables did not explain this association. The poor sensitivity, specificity, and positive predictive value of mucopurulent cervicitis suggests that this parameter is not a useful screening tool for chlamydial infection in pregnant women. However, mucopurulent cervicitis may be an indicator of increased risk for poor pregnancy outcome.