Early and serial endoscopic examinations were performed in patients with head injury to determine the actual incidence and course of the acute gastroduodenal lesions. Acute gastroduodenal lesions were found in 35 of 47 patients (75%). The lesions were found in 16 of 25 cases without obvious gastrointestinal [GI] bleeding. The lesions were mainly found in the stomach (78%) and of these lesions erosive gastritis was seen in the greatest frequency. Gastric ulcer was found in 11 patients. Erosive gastritis was found within 1 wk after the trauma, while gastric ulcer usually developed after 1 wk. Erosive gastritis was mainly located in the body of the stomach and usually healed within 10 days. Among 22 patients with GI bleeding, 3 had intractable bleeding. Steroid administration seemed to have little effect on the occurrence of acute gastroduodenal lesions.