Twenty-six cases of malignant cystosarcoma phylloides treated at The Charity Hospital of Louisiana were reviewed. No metastases to axillary lymph nodes was observed. The lesion appears to metastasize seldom, if ever, to lymphatics, and axillary dissection is seldom required. Local recurrence was common, however, and justifies wide resection of the primary. Mortality was related more to the size of the lesion than to other findings such as skin or muscle involvement. No lesion with less than three mitoses per ten high power fields and minimal stromal atypia proved fatal. Associated neoplasia was common, particularly in the opposite breast.