Acinic cell carcinomas of the Salivary Gland Registry, Institute of Pathology, University of Hamburg, West Germany, from 1965 to 1980 (n = 55) were evaluated retrospectively with respect to histologic, cytophotometric, and clinical data. The majority of the tumors (92.8%) were located in the parotid gland. Two thirds of the patients were female; one third were male. Mean age at primary diagnosis was 55.4 years. The tumors were graded into highly differentiated (76%) or less differentiated forms (24%) according to classic histologic and cytologic criteria. The clinical course was characterized by no recurrence in 15 cases; in 17 cases, recurrences developed, and 12 patients died of their tumor, some as late as 240 months after primary diagnosis. Differentiation showed a weak correlation with the clinical course. In 35 cases, nuclear DNA content of tumor cells was assessed cytochemically. The tumors were "diploid" or "near-diploid" in 34 cases; DNA content showed no correlation to the clinical course. As a result of long-term follow-up, it becomes evident that acinic cell carcinoma is prone to develop recurrences and metastases. Complete tumor removal during the primary operation seems to be important for controlling the disease inasmuch as the ostensible prognostic predictors evaluated here proved to be unreliable.