From January 1988 through December 1991, 81 men were examined for breast enlargement or mass in our Institute, by means of clinical examination, mammography, and US. The patients' age ranged 15-71 years (mean: 52 years). Of 81 studied patients, 71 had gynecomastia, 8 had adipomastia, 1 had an infiltrating ductal carcinoma, 1 an angiofibrolipoma and 1 a simple cyst. Both the carcinoma and the cyst were associated with gynecomastia. Three mammographic patterns of gynecomastia were observed: a glandular pattern in 42 cases (32 bilateral and 10 monolateral), a dendritic pattern in 12 (8 bilateral and 4 monolateral), and a nodular pattern in 15 (9 bilateral and 6 monolateral). On US, gynecomastia appeared diffuse in 54 patients and focal in 15. The infiltrating ductal carcinoma was clinically evident; no asymptomatic cancers were detected. Surgical biopsy was performed in 40 cases. A good correlation was observed between mammographic and US signs. The combined use of the two modalities can improve diagnostic accuracy. Biopsy must be performed in all questionable cases.