Purpose : The purpose of this study is to evaluate the radiologic features and clinical utility ofultrasonography 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 ofultrasonographic and mammographic findings was performed. Results : Causative factors of gynecomastia among the 40pathologically-proven cases were idiopathic or pubertal in 33 cases, related to male hormone deficiency in threecases 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 anddendritic marginated subareolar lesion without microcalcification in one. Ultrasonographically, a round smoothmarginated low echogenic lesion in the subareolar region was seen in five cases, a diffuse hyperechogenic patternwithout definite mass in two cases and an ill defined low echogenic lesion in one. Conclusion : The male breast issmall, 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.