The clinical features, treatment and outcome of 29 patients with oral Crohn's disease seen over a 6-year period have been reviewed. Findings on clinical examination included labial swelling (19 patients), buccal mucosal cobblestoning (11), linear ulceration (11), lumps (five), and mucosal tags (two). Eleven patients had multiple features. Eight patients developed symptoms within the first decade of life and nine patients had symptoms for more than 4 years before diagnosis; the mean age at diagnosis was 30 (range 6-78) years. Fourteen of these patients (48 per cent) have Crohn's disease elsewhere in the alimentary tract, and in nine patients the oral disease predated the development or detection of Crohn's disease at other sites. Eight patients (25 per cent) have required no specific therapy for their oral disease and 12 have been treated with systemic corticosteroids of whom three are steroid-dependent. No other pharmacological approach to treatment has been successful and elimination diets, tried by five patients, had no effect. Oral Crohn's disease has a characteristic naked-eye appearance, may be the first or only manifestation of Crohn's disease and usually improves with oral corticosteroid treatment.