The sonographic findings in four patients with gynecomastia are presented. The sonographic appearance is correlated with previously described pathologic and x-ray mammographic findings. Sonographically, early, focal gynecomastia appears as a triangular, hypoechoic mass in the retroareolar area. As gynecomastia become diffuse, it results in a hyperechoic increase in the glandular parenchyma. Awareness of the various etiologies and variations in appearance is important for the sonographic diagnosis of gynecomastia.