We analyzed the associations of colposcopic features with cervical and vaginal pathogens and with clinical diagnoses in randomly selected women attending a clinic for sexually transmitted diseases. Logistic regression models were used to adjust for coinfections. Significant associations (P less than 0.01) were found for endocervical mucopus with C. trachomatis, N. gonorrhoeae, and herpes simplex virus (HSV); ulcers/necrotic areas with HSV; "strawberry cervix" with T. vaginalis; increased surface vascularity with HSV; hypertropic cervicitis with C. trachomatis; and immature metaplasia with C. trachomatis and cytomegalovirus. Koilocytosis on cervical cytology was significantly associated with an atypical transformation zone on colposcopy, as well as with satellite lesions. The presence of leukoplakia and ectocervical asperities were also associated with koilocytosis. Awareness of these associations is important for colposcopists to identify patients who need specific microbiologic studies. Although colposcopy is generally used to evaluate patients selected because of abnormal cytology, our study suggests that colposcopic examination could be a useful adjunct to cytology in screening for a variety of cervical and vaginal infections.