In the present study, virtually all of 225 patients suffering from Crohn's disease of the lower gastrointestinal tract (small and/or large bowel) were subjected to endoscopic examination of the upper gastrointestinal tract (esophagus, stomach, duodenum); while histologic examination of the upper gastrointestinal tract was performed in a portion of the patients (54 initial esophageal, 221 initial gastric and 210 initial duodenal examinations). Statistical evaluation of the findings from the upper gastrointestinal tract revealed that: Endoscopic lesions were observed in the esophagus of 15%, the stomach of 49%, and the duodenum of 34% of the 225 Crohn's disease patients. Of the 54 patients from which esophageal biopsies were taken, 31 (57%) revealed histopathologic alterations. Of the 221 patients from which gastric biopsies were obtained, 60% revealed histopathologic alterations; the rate was 53% in the 210 patients from which duodenal biopsies were taken. Calculated from the present data, noncaseating granulomas, i.e., Crohn's disease, were present only in the stomach of 29.4% of the patients, only in the duodenum in 3.4% of patients, and in both the stomach and duodenum in 4.9% of patients. Gastric granulomas were confined to the region of the stomach body and fundus in 3.4% of the patients from which gastric biopsies were obtained and to the antrum in 15.6% of the respective patients. Both gastric regions were involved in 8.3% of the respective patients. The incidence of gastric granulomas was significantly increased in young patients, patients with enterocolic manifestations of Crohn's disease, and those with brief duration of disease. Patient sex or previous drug therapy had no effect on the incidence of granulomas. The most frequent endoscopic findings in the stomach of patients with Crohn's disease were mucosal edema, mucosal redness, and acute or chronic erosions. Only chronic erosions were of significant predictive value for the presence of granulomas, i.e., diagnosis of Crohn's disease. The most frequent endoscopic lesion in the duodenum was mucosal redness, followed by mucosal edema and aphthous lesions. Ulcers, stenosis, and mucosal redness had significant predictive values for the presence of granulomas.