We compared the clinical and epidemiological characteristics of 89 women with pelvic inflammatory disease (PID) seen at a clinic for sexually transmitted diseases during 1982 and 1983. Patients were classified into four groups by having endocervical cultures positive for Neisseria gonorrhoeae only (24), Chlamydia trachomatis only (16), both organisms (14), or neither organism (35). More women with cultures positive for N gonorrhoeae were black (p less than 0.005), had a sexual partner with gonorrhoea (p less than 0.005), and had a purulent vaginal discharge (p less than 0.05). No other significant differences were found between groups regarding age, exposure to a sexual partner with non-gonococcal urethritis, history of trichomoniasis, parity, use of antibiotics, contraceptive history, duration of abdominal pain, relation of pain to the phase of the menstrual cycle, abdominal rebound tenderness, reproductive tract signs, or febrility. In women presenting to outpatient clinics, PID tends to be mild and the diagnosis unreliable. Though C trachomatis is emerging as an important aetiological agent, we found no clinical indicators that could distinguish chlamydial from gonococcal PID.