PURPOSE: The purpose of this study is to evaluate the radiologic features and clinical utility of ultrasonography and mammography in cases of gynecomastia. MATERIALS AND METHODS: This study involved 40 men inwhom gynecomastia had been pathologically diagnosed by surgical incision. In 21 cases, a retrospective analysis of ultrasonographic and mammographic findings was performed. RESULTS: Causative factors of gynecomastia among the 40 pathologically-proven cases were idiopathic or pubertal in 33 cases, related to male hormone deficiency in three cases and to chronic liver disease in four. Bilateral involvement was seen in 14 cases, and unilateral involvementin 26 ; among unilateral cases, right side was involved in 10 cases, and the left side in 16. Mammographically, asubareolar discoid lesion was present in 12 cases, diffuse increased breast density was seen in five cases and dendritic marginated subareolar lesion without microcalcification in one. Ultrasonographically, a round smooth marginated low echogenic lesion in the subareolar region was seen in five cases, a diffuse hyperechogenic pattern without definite mass in two cases and an ill defined low echogenic lesion in one. CONCLUSION: The male breast is small, so in cases of gynecomastia, ultrasonography is an effective diagnostic modality. Mamography will, however, be helpful in the detection of microcalcification in cases of gynecomastia seen on sonography.