A 76-year-old man developed jaundice and was hospitalized in January 2002. A 3 cm tumor was found in the head of the pancreas by abdominal CT, and the patient underwent laparotomy. The tumor was histologically diagnosed as a well-differentiated adenocarcinoma, and showed extensive invasion to the portal vein (T4NXM 0 Stage IV a). Incisional biopsy and hepaticojejunostomy were performed. On the basis of a drug sensitivity test, chemotherapy with 800 mg/m2/week gemcitabine was administered. The patient showed prolonged NC without any symptoms for 22 months, although the CEA and DUPAN-2 levels gradually increased during this time and massive ascites were detected in a routine abdominal CT at 22 months postsurgery. The patient died after 25 months of chemotherapy. Here we report a case of unresectable pancreatic cancer treated with gemcitabine on the basis of a drug sensitivity test.