A mammographic and clinical screening for breast cancer started in June 1987 in the Health District of Brescia, Northern Italy, including the town and 23 surrounding municipalities. This paper describes the organization and the results of the first 12 months of screening. Of 7791 invited women aged 50-60 years, 5217 (67%) agreed to participate. There was a trend for response rates to decline with increasing age and education. Of the 5217 women examined, 66 (1.3%) were referred for biopsy and 64 (1.2%) underwent this procedure. A histologically confirmed malignancy was found in 42 women, corresponding to a prevalence of 8.1/1000. Positive predictive value of the screening was 65.6%. Among the 42 breast cancers, 4.8% were carcinoma in situ and 42.9% invasive tumors up to 10 mm in size. According to the p-TNM classification, 92.9% of all cancers were either TIS or in stage T1, 4.8% were in T2 and one tumor was classified in T4. Lymph node involvement was assessed in 41 cases, and 71.4% of all cancers detected by screening were negative for lymph node metastasis. In comparison, the classification of tumors found in women of the same age group and living in Brescia, histologically diagnosed in the urban hospitals during 1986, one year before the beginning of the screening, was as follows: 7.1% carcinoma in situ, and 16.7% invasive tumors up to 10 mm in size. 38.1%, 2.4% and 2.4% of all tumors were in stages T2, T3 and T4 respectively.