The causes of extra-arterial dislocation of indwelling catheter (EAD), which was one of the serious complications in arterial infusion chemotherapy, were examined. Subjects were six cases of EAD among the 45 cases of gastric cancer with liver metastases treated with hepatic arterial infusion chemotherapy. According to the route of cannulation, EAD occurred more frequently in the cases of cannulation via gastroduodenal artery (18.5%) than in those via subclavian artery (5.5%). Concerning the drugs and their administration, all cases of EAD were treated by continuous injection of 5-fluorouracil (5-FU). Main symptoms of EAD were high fever, abdominal pain and anemia, which developed after administration of total doses from 4.0 g to 30.5 g of 5-FU. In conclusion, it was strongly suggested that arterial destruction due to the toxicity of 5-FU caused EAD in hepatic arterial infusion chemotherapy, especially in cases of cannulation via gastroduodenal artery due to the high concentration of 5-FU in a limited part of the arterial wall.