The clinical and pathologic findings of 17 hamartomas of the breast were studied. All neoplasms were evident as clinically and mammographically discrete masses. The pathologic findings were varied and included circumscribed fibrocystic disease, adenolipoma, fibroadenoma with fat and fibroadenoma with lobules. The heterologous elements identified were cartilage and smooth muscle. All lesions were treated by simple excision. In this study, four different microscopic patterns of hamartoma are described and the necessity for a close clinicopathologic correlation is pointed out in the diagnosis of this lesion.