Phyllodes tumors are rare lesions of the breast with unpredictable behavior. A review of 18 patients with phyllodes tumors was performed to determine if pathologic and cellular characteristics correlated with clinical behavior and to determine the influence of the extent of the operation performed on clinical outcome. Local excision, primarily breast biopsy, was performed in 14 of the 18 patients. At a median follow-up of 26 months (range: 3 to 164 months), there have been three recurrences, two in patients with low-grade tumors and one in a patient with a high-grade lesion, who eventually died as a result of widespread metastases. Recurrences were noted from 2 to 56 months after the original operation. Poor correlation was noted between standard pathologic criteria or flow cytometry and the risk of recurrence. Phyllodes tumors exhibit a wide spectrum of clinical behavior. Most patients will not experience a recurrence, but even small, low-grade tumors may recur if inadequately excised. Occasional patients have extremely aggressive disease that may result in death.