Polymorphous low-grade adenocarcinoma, also known as terminal duct or lobular carcinoma, was first described in two clinical case series in 1983. Before that time most of these neoplasms were diagnosed as benign salivary gland neoplasms including pleomorphic adenomas, variants of monomorphic adenomas, or salivary malignant conditions including malignant pleomorphic adenomas, adenoid cystic carcinomas, and adenocarcinoma not otherwise stated. This neoplasm with few exceptions originates in minor salivary gland tissue of the posterior hard and soft palates or buccal mucosa. It is characteristically slow to enlarge; clinical reports show the neoplasm present for many years before diagnosis. We have evaluated the clinical and microscopic features of 15 cases from the archives of The University of Iowa Surgical Oral Pathology Laboratory and added these to published case reports. A total of 204 cases were evaluated with a female/male ratio of almost 2/1. Forty-nine percent originated in palatal mucosa. Polymorphous low-grade adenocarcinomas arising from pleomorphic adenomas or de novo have been reported within major salivary glands and outside the oral cavity. A 17% recurrence rate was found with a regional metastasis rate of 9%. Five cases had multiple recurrences, and 13 recurrences were at or beyond 5 years after the initial diagnosis. Regional node metastases were identified at the time of initial treatment or at the time of recurrence in 9% of cases in which follow-up data were specified.