In a recent 11.5-year period from January 1989 to July 2000, six patients underwent surgery for primary adenocarcinoma of the duodenum, excluding the papilla of Vater. These cases accounted for 0.43% of all cases of gastrointestinal cancer operated on at the hospital. Common complaints were caused by stenosis and bleeding in most cases. There lesions were situated in the bulb in two cases, in the second portion in three cases, and in the third portion in one case. Macroscopically, five tumors were ulcerative type and the remaining one superficial protruded type. Microscopically, four of the six tumors invaded the pancreas with lymphatic invasion and lymph node metastasis. In half of the cases, lymph node No 13 was involved by the cancer, and lymph nodes No 6, 12, 14a, and 17 were also involved. Two patients whose cancer cells invaded the perineural space died of local recurrence of cancer in early postoperative course. In terms of lymph node involvement, gastroduodenectomy with lymphadenetomy of the hepatoduodenal ligament or pancreatoduodenectomy would be necessary for treatment of advanced carcinoma of the bulb, and pylorus-preserving pancreatoduodenectomy for that of the second and third portions.