Eighteen cases of sarcomas of the breast are reported. Cases could be divided into two groups histogenetically. Group A, malignant cystosarcoma phylloides (14 cases); and Group B, pure sarcomas (4 cases). The malignant cystosarcoma phylloides occurred in the forth decade, had linger duration of illness invariably followed by sudden increase in the size of the tumor, had a striking mucoid and slimy look grossly, and showed discernible epithelial elements histologically. In the event of their recurrence the ductal elements were not seen microscopically. Contrarily, Group B cases presented in the sixth decade were rapidly growing from the beginning, and grossly were fleshy and haemorrhagic. Microscopically these did not reveal any epithelial component. There was poor correlation between cytologic malignancy and the biologic behavior in Group A. Mode of treatment seems more important in determining the subsequent course of the disease. Simple mastectomy with follow-up appears to be adequate in the majority of cases.