The California Department of Health Services conducted a cervical cancer screening program in 12 counties where local health agencies provided the screening services. A major purpose of the study was to screen women at high risk of cervical cancer and to assure that women with abnormal results on cervical cytology testing obtained appropriate diagnostic workup and treatment. A total of 34,318 women were screened, and 7,811 returned for up to 3 annual rescreening examinations. Final cytologic results were 33,658 normal, 100 unsatisfactory, and 560 abnormal smears. Of the abnormal smears, 484 were indicative of cervical dysplasia, 41 of in situ cervical cancer and 22 of invasive cervical cancer. In 13 women, endometrial cancer was suspected. Complete followup information on diagnostic evaluation and treatment was obtained for 80 percent of the women with abnormal Pap test results. Histological confirmation of neoplasia was reported for 173 women. The diagnoses were cervical dysplasia in 108, cervical cancer in 58 (49 in situ, 9 invasive) and endometrial cancer in 7. The program reached greater proportions of older women, the less affluent, women of Spanish origin and oriental women and a smaller proportion of blacks than were present in the general female population of California.