Of 1267 women attending a gynaecology clinic, who were screened for the presence of Chlamydia trachomatis, 45 (3.6%) were found to be infected. Infection with C. trachomatis was more common in women who were less than or equal to 25 years of age, unmarried, nulliparous, requesting termination of pregnancy, using oral contraception as opposed to barrier methods, and who had cervical ectopy or cervicitis. Using contact tracing techniques 35% of male sexual partners of women who harboured C. trachomatis were also found to be infected. 86% of these men were symptomless. Asymptomatic chlamydial infection is common in men as well as women. Selective screening to identify women at risk of infection and the use of contact tracing to identify symptomless men with chlamydial infection are shown to be of value.