PURPOSE: To define and correlate characteristic sonographic and pathologic findings in men with gynecomastia. MATERIALS AND METHODS: We reviewed medical records and sonographic findings of 26 patients with pathologically proven gynecomastia. All of the chief symptoms, physical findings and causes were categorized. Characteristic sonographic patterns of gynecomastia were analyzed and compared with pathologic findings. RESULTS: Gynecomastia was most common in the 20- to 40-year-old age group (50%) 6;palpable mass was found in 62% of all those cases. Gynecomastia was unilateral or asymmetrical in 22 men (85%), and was caused idiopathically in 21 (81%). The characteristic sonographic patterns correlated with pathologic findings were as follows : (1) focal subareolar smooth oval (or triangular) indistinct margined homogeneous hypoechoic(or isoechoic) patterns were found in 14cases (54%). Eight of these (57%) were of the florid type of gynecomastia (67%) ; (2) diffuse homogeneous hyperechoic (or isoechoic) patterns were found in five cases (19%) ; four of these (80%) were of the intermediate or fibrotic type : (3) involuting female breast parenchymal patterns were found in seven cases (27%), of which six(86%) were of the intermediate or fibrotic type. CONCLUSION: The characteristic sonographic patterns of gynecomastia correlate closely with pathologic types related to the duration of the condition. Ultrasonography isa useful primary diagnostic modality for the evaluation of gynecomastia.