In a 7 1/2-year period (from 1 January 1980 to 30 June 1987), 997 patients with gastric cancer underwent gastric resection at the Department of Surgery, Matsuyama Red Cross Hospital, Japan. We studied clinicopathologically 83 patients (182 lesions) with synchronous multiple gastric cancer and compared them with patients who had solitary cancers only in the same period. We found that elderly men had a relatively high incidence of multiple gastric cancer, and that early cancer of the elevated well differentiated type was the most common. Of the 182 lesions, as many as 42 (23.1 per cent) were missed in the preoperative examination. Eighteen of these 42 lesions were found only with the aid of a microscope in sections almost incidentally excised. Small flat lesions tended to be missed. We should always be conscious that other gastric lesions may be present when treating patients with gastric cancer.