A case-control study of 293 patients with in situ cervical cancer and 801 community controls was conducted between 1982 and 1984 in five geographic areas in the United States. Relative risk (RR) was elevated among women reporting multiple sexual partners (RR for ≥5 partners = 5.0), a history of an abnormal Papanicolaou smear (RR = 5.0), interval since last Papanicolaou smear (RR for ≥10-year interval versus 0- to 2-year interval = 4.1), use of oral contraceptives (RR for ≥ 10 years use = 1.4), a history of nonspecific genital infection (RR = 2.6), and smoking (RR for current smokers = 1.9). Risk was low among diaphragm users (RR for >2 years use = 0.5). Neither age at first coitus nor number of births was predictive of risk of in situ disease. Comparisons between this analysis and risk factors previously identified for invasive cervical cancer in this same study indicate that the risk factors were quite similar.