A 14-year-old case was reported with a primary postbulbar duodenal ulcer, which was confirmed by barium meal study and duodenoscopy. In the preoperative study, the patient showed marked gastric hyperacidity: maximal and peak acid output were 0.980 and 1.434 mEq/kg/hr, respectively. As previously described, hyperacidity appears to be a main factor in the pathogenesis of postbulbar duodenal ulcer. Fasting and postprandial serum gastrin secretion was not thought to be responsible for gastric hyperacidity in the present case. Upon histological investigation, the operatively resected stomach did not suggest a possible relationship between hyperacidity and an enlarged parietal cell mass.