A case-control study was conducted in Utah between 1984 and 1987 to examine risk factors for cervical cancer. Interviews were completed with 266 histologically confirmed carcinoma in situ and invasive squamous cell cervical cancer cases who were categorically matched by age to 408 controls. Among the factors identified as altering risk for cervical cancer, after adjustment for age, education, church attendance, and cigarette smoking, were: having numerous sex partners (odds ratio (OR) = 8.99 for 10 or more partners); the current mate having several sex partners (adjusted OR for 10 or more partners = 8.62); using foam or jelly as a contraceptive method (OR, adjusted for number of sex partners, = 0.44); reported Trichomonas infection (OR, adjusted for number of sex partners, = 2.10); and herpes simplex virus type 2 infection as determined by 2:1 neutralization index values above 100 (OR = 2.70). A protective effect was noted from the use of diaphragms (OR = 0.67) or condoms (OR = 0.53) in women who reported more than one sex partner. These data support the hypothesis that cervical cancer is a sexually transmitted disease.