A 68-year-old woman with severe postmenopausal osteoporosis was referred because of a 6-month history of erosive mucositis of the hard palate, accompanied by intense pain and dysphagia. The patient had an edentulous superior arch and wore a removable upper denture. Examination showed a large oval ulceration of the hard palate, 2 by 3 cm in diameter, with regular margins and a necrotic center (Panel A). Previous unsuccessful treatment of the lesion included systemic and topical corticosteroids, antibiotic agents, and antimycotic agents. Cytodiagnostic and microbiologic evaluations, including those for cancer, herpesviruses, and Treponema pallidum, were unrevealing. The patient did not report using nonsteroidal antiinflammatory drugs, but she did report taking oral alendronate (10 mg per day) for 8 months for severe osteoporosis. The patient reported that she had difficulty swallowing tablets and that she held the tablet in her mouth behind her upper denture plate before being able to swallow it. Contact stomatitis due to alendronate was diagnosed. The patient was instructed to swallow the alendronate without holding the tablet in her mouth and to always remove the denture beforehand. In 2 weeks, the mucositis had improved substantially (Panel B).