An epidemiologic study was performed 1) to estimate the occurrence of epithelioid granulomas in the appendix wall among patients in whom an appendectomy had been performed, 2) to identify patients with granulomas in the appendix who had symptoms and history compatible with Crohn's disease, and 3) to estimate the long-term prognosis. Within a 5-year period 6051 patients in Copenhagen County underwent appendectomy. Six patients (0.1%) had epithelioid granulomas of the appendix (0.2 per 10(5) inhabitants per year). Follow-up of the six patients for 9-11 years (median, 9.5 years) showed that all had been free of gastrointestinal symptoms since the operation. Among the 373 patients diagnosed as having Crohn's disease in Copenhagen County between 1962 and 1987, 3 patients had their disease initially confined to the appendix. Follow-up in these patients showed no recurrence within a median of 6 years (range, 4-7 years). Patients with epithelioid granulomas of the appendix have an excellent long-term prognosis, which could be explained by the fact that the condition seems to be unrelated to Crohn's disease.