Of 10,000 mammographies done over a 9-year period, 16 cases of hamartoma of the breast were diagnosed. The entity is a well delimited mass composed of dysplastic-appearing mammary tissue admixed to fat. It can be readily recognized and should not be confused with fibroadenoma or mammary dysplasia. The accuracy with which it can be diagnosed by mammography makes possible the avoidance of surgical excision in selected patients.