All mammary lesions diagnosed at the Institute of Pathological Anatomy of the University of Modena have been systematically filed since 1990 and reported in a bulletin, which is issued twice a year and delivered to health operators. So far, 5.188 cases of breast lesions, comprising 1.999 non-neoplastic pathologies, 1.040 benign tumors, 1.943 primary malignant neoplasms and 206 recurrences, have been filed. During the quinquennium 1990-1994, a progressive numerical reduction in diagnoses of non-neoplastic lesions coupled to an increase of benign tumors has been observed, whereas the number of primary malignant tumors has not changed. In particular, a statistically significant increase in diagnoses of carcinoma-in-situ and of fibrocystic disease associated with moderate-risk lesions (atypical hyperplasias) has been detected, whereas the number of cases of single fibrocystic disease has decreased. This reduction, however, is not significant. A slight increase of breast carcinomas smaller than 1 cm and 2 cm, coupled to a decrease of those exhibiting dimensions between 2 and 5 cm, has been found. The collection and systematic analysis of cases of mammary lesions appears to represent a useful tool to study the incidence of different breast pathologies in the general populations. It can also be viewed as a simple way to test the reliability of diagnostic methods used for selection of surgical cases.