The presence of mucosal Darier disease (keratosis follicularis) was evaluated clinically and histologically in four consecutive patients with moderate to extensive cutaneous manifestations of this disease. Fiberoptic endoscopy demonstrated hypopharyngeal or laryngeal involvement or both in each patient. A dearth of corps ronds and grains in these anatomical regions was observed histologically. The routine evaluation of mucosal involvement in Darier disease should result in a higher incidence of hypopharyngeal and laryngeal lesions than is currently known. Furthermore, the recognition of hypopharyngeal and laryngeal involvement with Darier disease must be emphasized because of the clinical similarity to leukoplakia and squamous cell carcinoma.