Five hundred sixty-eight adolescent female patients receiving routine gynecologic care at urban clinics were screened by culture for Chlamydia trachomatis infection at both the urethra and endocervix. Culture results for 562 were available from either or both sites. Positive cultures were obtained from 139 (25%). Urethral infection was not associated with either urinary tract symptoms or sterile pyuria, but urethral or endocervical infection was associated with cervical friability (P = less than 0.0001), endocervical mucopus (P = 0.0001), cervical erythema (P = 0.0002), and cervical ectopy or erosion (P = 0.01). Increased chlamydial infection rates were associated with older age (P = 0.01), history of more frequent intercourse (P = 0.01), and history of more than one lifetime partner (P = 0.023), with a marginal association for being black (P = 0.05). Method of contraception, reason for attending clinic, age at menarche, age at first intercourse, years sexually active, number of sexual partners in preceding 6 months, parity, and prior history of sexually transmitted disease were not associated with having chlamydial genitourinary infection.