Sixty patients with mucoepidermoid carcinoma of salivary gland origin were studied. The pathologic findings and the clinical course were examined separately and then correlated. The tumors are classified as either well, moderately, or poorly differentiated. The criteria used to classify the lesions are discussed, and pathologic features are illustrated. The most important factors in the prognosis are: 1. degree of histologic differentiation, and 2. presence or absence of tumor on the lines of surgical excision. Recurrences correlated with the degree of histologic differentiation. Only one of 31 patients (3%) had a recurrence when careful examination of the surgical specimen failed to demonstrate tumor on the lines of resection. In contrast, 19 of 28 patients (68%) with tumor on the surgical margin had a recurrence. The other 9 patients had no recurrence, having been given immediate subsequent treatment. Recommendations made for therapy are based on the histologic grade of the tumor and on examination of surgical lines of resection.