Adenomatoid hyperplasia is a rare cause of swelling of the oral minor salivary glands, but is of significance because of its clinical resemblance to salivary gland tumors. The histologic appearance is one of benign hyperplasia and hypertrophy of the minor mucous glands. The clinical and histologic features of 20 new cases are reported, 19 of which occurred in the hard or soft palate. The cause of adenomatoid hyperplasia has hitherto been unclear, but the observation that 14 subjects were tobacco smokers or denture wearers, or both, suggests chronic, local trauma may be an important factor in the development of the condition.