We conducted a clinical study on a newly developed large diameter vascular graft (Triplex^®, Terumo Corporation, Tokyo, Japan) with a non-biodegradable material used as sealing material, to evaluate its effectiveness and safety. Triplex^® grafts were implanted in 170 patients with either aneurysmal or occlusive arterial disease in either the thoracic artery, abdominal artery or iliac arteries, between October 2001 and March 2003. The patients consisted of 141 men and 29 women with an average age of 69.0±10.0 years old (mean±SD). In 82 patients, Triplex^® was implanted for the thoracic artery area, in 88, for the abdominal artery area. The cumulative graft patency rate 12 months after implantation was 100.0% in each area, there was no any abnormality such as occlusion or rupture from the trunk of Triplex^®. The distension ratio, which is the index of the dilatation resistance, was 1.03±0.06 as a whole (n=139), 1.03±0.06 in the thoracic artery area (n=73), 1.03±0.06 in the abdominal artery area (n=66). In other words the dilatation of Triplex^® was hardly observed. As manipulability during the operation, the following characteristics were evaluated; anastomosis, resistance to fraying, hemorrhage, conformability with the host vessel. Triplex^® was evaluated as “good” in 75% of all items accounted for 75% or more. A transitory rise thought to be due to the surgical stress immediately after the operation because of the change of temperature and laboratory findings (CRP, WBC) between implantation and discharge was observed, but then recovered to the normal levels of each patients at discharge and the re-elevation was not recognized. In 90 patients, 277 adverse events occurred. Although in 33 adverse events in 21 patients a causal relation with Triplex^® could not be excluded, most of them were already known events as complications which could occur after operation on the aorta. Therefore, it was confirmed that Triplex^® has certain advantages: 1) good manipulability, 2) good patency and dilatation resistance, 3) no inflammatory reaction related to Triplex^®, as a graft for the aorta.