Forty-seven cases of malignant mixed tumor (MMT) arising in major and minor salivary glands are presented. By definition, all these lesions contained both a benign mixed tumor (BMT) as well as a malignant neoplasm, usually a poorly differentiated carcinoma. In some cases, the carcinoma developed in a previously untreated salivary gland mass which was known to have been present for many years, others evolved in a recurrent previously resected BMT and still others originated in a previously undetected BMT. Adverse prognostic factors included: carcinomatous involvement of the resection lines, perineural invasion, metastases in lymph nodes, and origin in a major salivary gland. Lesions arising in the palate had a better prognosis as compared to major salivary gland tumors. Some patients died of locally uncontrollable tumor and others because of metastatic disease. Local recurrences of MMT were seen frequently; 18 patients (38%) had a total of 32 local recurrences. Of patients followed five years or more, seven (35%) had died of tumor, 11 (55%) had no evidence of disease, and two (10%) had died of other causes. Prolonged follow-up is required because recurrences and death from tumor may be seen many years following the diagnosis of MMT. Recommendations for therapy are made. Criteria for differentiating MMT from recurrent BMT and from cylindromatous carcinoma are discussed.