Behçet oral ulceration (BOU) is described as being indistinguishable from conventional recurrent oral ulceration (ROU). A clinical comparison between 38 Behçet patients and 38 control ROU cases was effected by completion of a standard questionnaire. Behçet patients reported an increased number of concurrent ulcers and involvement of the soft palate and oropharynx. No differences were detected with respect to duration, frequency, age of onset or family history. In addition, photographs of BOU in 15 patients revealed the concurrence of atypical aphthous and herpetiform varieties. Number, site and appearance of oral ulceration may therefore provide diagnostic features for the development of Behçet's disease.