Needle aspiration cytology, immunocytochemistry and electron microscopic findings are described in a case of rare breast carcinoma with bizarre, malignant giant cells in a young female under age 30. The malignant tumors were found in both breasts; the first one was diagnosed when the patient was 23 years of age and the second one in the contralateral breast four years later. Based on our present findings, and in keeping with a similar case recently described by us as occurring in an elderly female, we thought that the bizarre giant cells in this rare breast carcinoma were of epithelial origin. The differential diagnosis of other conditions that may be associated with giant cells in breast aspirates is discussed.