The early detection of breast cancer is of primary importance, as one method which many reduce the unacceptably high mortality rate associated with this disease. In fact, it is well stated that the most concrete possibility of therapeutic success in the treatment of breast cancer is represented by early treatment, while the disease is still localized. Then a screening program is necessary in asymptomatic women, to diagnose the disease as early as possible even in case of non palpable lesion. Mammography is nowadays the most specific and sensitive investigation for clinically occult breast cancer. In this study we searched for mammographic findings with the best predictive value for cancer and we tested the most careful techniques for preoperative localization and surgical biopsy of nonpalpable breast lesions. Seventy-one asymptomatic women (age range: 31-76 years, mean: 53.6) underwent stereotaxic needle localization to perform surgical biopsy of mammographically suspicious but nonpalpable breast lesions. Mammographic findings were classified as: a) well defined and smooth bordered opacities (11.3% of cases); b) poorly defined, irregular, spiculated and stellate opacities (32.4% of cases); c) lowly suspicious microcalcifications, larger, rounder, fewer in number (19.7% of cases); d) highly suspicious microcalcifications, with irregularities on shape, density and size described as clustered and polymorphic (36.6% of cases). Cancer was found in 22 cases (31%); 12 of those (54.5%) were associated with highly suspicious microcalcifications, 10 of those (45.5%) were associated with stellate and poorly defined opacities.(ABSTRACT TRUNCATED AT 250 WORDS)