Clinicopathologic features of 319 patients who underwent gastrectomy for adenocarcinoma of stomach were studied whether disease involved duodenum or not. Thirty-eight patients (11.9%) had duodenum invasion. Gastric carcinoma with duodenal invasion was most often Borrmann III or Borrmann IV (65.8%) type, with pylorous invasion by endoscopy (39.5%), large tumor size (73.7% > or = 5cm), lymph node metastasis (78.9%), serosal invasion (97.4%) and the incidence of the resection line not being free was high (13.2%). Duodenal invasion was most often (55.3%) direct through the deep layer or through lymphatics or venules. We need to pay more attention to finding duodenum invasion. More than 3 cm width of duodenal resection is recommended if duodenum invasion is suspected.