Six cases of polymorphous low-grade adenocarcinoma (terminal duct adenocarcinoma) of the minor salivary glands are presented. In all but one there was a history of a painless intra-oral mass of fairly long duration. The histopathological appearances were characterized by cytological uniformity in a variety of morphological patterns, including tubular, solid, fascicular and cribriform areas. At a cellular level, the tumours possessed regular, often vesicular nuclei and generally eosinophilic cytoplasm. Five of the patients are still alive, although one had recurrent disease 16 years after her original operation; none died of their tumour. These findings are compared with those of six salivary adenoid cystic carcinomas, a neoplasm with many similar histological features, but with a much worse prognosis. The microscopic differences were mainly cytological and, to a lesser extent, morphological. The immunohistochemical reactions of the two tumours were not sufficiently dissimilar to be of practical value. Polymorphous low-grade adenocarcinoma has only rarely been reported in Britain, but we believe it deserves wider recognition as a distinct clinicopathological entity and, in particular, separation from adenoid cystic carcinoma.