Fifty-one cases of acinic cell carcinoma (ACC) arising in major and minor salivary glands are reported (primary sites: parotid 37, submandibular, six, and oral cavity, eight.) These lesions usually produced painless slowly growing masses. Of 49 patients with follow-up information, 17 (35%) developed local recurrences following original surgical resection, and two (4%) had locally persistent disease. At last follow-up, 27 patients (55%) never had a recurrence, seven (14%) had experienced local recurrences but the tumors were apparently controlled by further surgical excisions, five (10%) were living with persistent disease, and 10 (20%) had died (one due to local tumor and nine due to metastases, usually to bones and lungs). The determinate 5-, 10- and 15-year survival rates were 78%, 63%, and 44%, respectively. Prognostic factors included: demonstrable tumor on lines of surgical excision, involvement of deep lobe of parotid, size of primary lesion, degree of mitotic activity and nuclear atypia, infiltrative rather than circumscribed borders, and lymph node involvement. Local recurrence was associated with an increased incidence of locally uncontrollable and metastatic disease. Type of initial therapy correlated with prognosis. Locally recurrent or persistent tumor was found in 14 of 15 patients treated with limited local excisions (including one biopsy only). Recurrences were seen in only three of 28 patients treated by wide local excisions and in two of six following radical en bloc resections. Seven of 17 patients with local recurrence were apparently cured by further more extensive resection. Radiotherapy did not appear effective in controlling these neoplasms.