In the Varese province (409,142 female inhabitants in 1981), which has been covered by a cancer registry since 1976, cytologic screening for cervical cancer began in the early sixties in the municipality of Busto Arsizio (41,818 female inhabitants in 1981) and subsequently spread to the rest of the province. The distribution by age of cytologic smears and of detected in situ cancer reveals a more frequent attitude to be screened for women aged between 25 and 54 years. Overall, the incidence rate (world standardized) for invasive cancer in the province decreased from 10.3/100,000 women-year in the period 1976-81 to 7.5/100,000 in 1982-87. In Busto Arsizio a survey of the hospital archives has been carried out to identify the cases of cervical cancer diagnosed from 1966 to 1985: in this 20-year period, the incidence of cervical cancer decreased markedly, but only in those ages frequently screened. In the rest of the province, for the first period of cancer registration (1976-81), the incidence was significantly higher than in Busto Arsizio, especially for ages 35-64. Subsequently, between 1982-87, the cervical cancer incidence was low in both areas. For the period 1976-87, no difference for carcinoma in situ registration rates was observed between the two populations studied. Actually by 1976, when the Lombardy Cander Registry began its activity, the screening was diffuse throughout the province. These observations are consistent with the preventive effect of screening activity.