The clinical and pathologic features of 13 patients with pure liposarcomas of the breast and seven patients with liposarcomas that had arisen in cystosarcomas are reviewed. Metastases occurred in three of the 13 patients with pure mammary liposarcomas, and two women died of tumor. One of the patients with a liposarcoma that had arisen in a cystosarcoma had a local recurrence one year after diagnosis but was subsequently lost to follow-up study. Fourteen of the 20 patients for whom follow-up information was available for as long as 14 years had no evidence of recurrence. Features associated with the development of recurrence, based on the cases studied here and previous reports, included the pleomorphic liposarcoma pattern and an infiltrative margin. Features associated with tumor-free survival included the well-differentiated liposarcoma pattern, male gender (two patients), and a circumscribed microscopic tumor margin. There were no axillary lymph node metastases. Follow-up data indicate that complete surgical excision of tumor with tumor-free margins is necessary, but total mastectomy and removal of the axillary tail are not required unless these procedures are needed for complete excision.