PURPOSE: To evaluate the sonographic and mammographic features of apocrine metaplasia of the breast. MATERIALS AND METHODS: We retrospectively evaluated the sonographic and mammographic findings of 16 lesions that were diagnosed with only apocrine metaplasia after mammotome excision. The age ranged from 27 years old to 57 years old (mean age; 40 years old). The sonographic features were interpreted by the ACR BI-RADS (American College of Radiology Breast Imaging Reporting and Data System) for shape, orientation, margin, boundary, echo pattern, posterior acoustic feature, calcification and special cases. The mammographic features were interpreted by the ACR BI-RADS (American College of Radiology Breast Imaging Reporting and Data System) for breast composition, shape, margin, density and calcification. RESULTS: Sonographic features were that the shapes were oval (n = 16) in 100%. The orientation was parallel (n = 15) in 94%. The margins were circumscribed (n = 8) in 50% and microlobulated (n = 8) in 50%. The echo patterns were hypoechoic (n = 8) in 50%, complex (n = 5) in 31% and anechoic (n = 3) in 19%. Posterior acoustic enhancement was seen in 69% (n = 11). There was internal microcyst (n = 4) in 25%. There was no calcification. Mammography performed for 12 cases demonstrated negative findings (n = 10) for 83%, obscured hypodense mass (n = 1) for 8% in 11 cases of breast composition 3 and 4, and circumscribed isodense mass (n = 1) for 8% in one case of breast composition 2. There was no calcification. The final assessment was category 4a (n = 7) in 44%, category 3 (n = 6) in 38% and category 2 (n = 3) in 19%. CONCLUSION: Although sonographic and mammographic features of apocrine metaplasia are occasionally suspicious malignancy such as microlobulation and complex echo. We consider the possibility of apocrine metaplasia if masses show internal microcyst and abrupt boundary.