Styrene-maleic acid neocarzinostatin (SMANCS) sometimes causes hepatic vascular side effects, including arterial stricture, obstruction, and arterio-portal shunt. A total of 128 intra-arterial SMANCS injection treatments, performed for 89 patients with hepatocellular carcinoma, were analyzed to determine the relationship between angiographic findings and subsequent hepatic vascular injuries. After SMANCS therapy, hepatic arterial stricture or obstruction occurred in 5 patients (5/128; 3.9%), arterio-portal shunting in 12 (12/128; 9.4%), liver shrinkage in 4 (4/128; 3.1%), and cholangitis or biloma in 2 (2/128; 1.6%). Among 23 patients whose plain abdominal X-ray films just after SMANCS injection showed Lipiodol retention in the hepatic artery, 5 patients developed arterial obstruction, 10 developed arterio-portal shunt, and 2, cholangitis or biloma. Among 26 patients with Lipiodol retention in the portal vein, 4 developed hepatic lobe atrophy with aggravation of liver function. Among 3 patients with Lipiodol retention in both the hepatic artery and the portal vein, 1 developed arterio-portal shunt. In 76 treatments without excessive Lipiodol retention, only 1 of the patients developed arterio-portal shunt. Excessive retention of Lipiodol in hepatic vascular beds just after SMANCS therapy was significantly associated with future vascular side effects (22/52 vs 1/76; P < 0.0001). Lipiodol retention in arteries just after SMANCS injection was closely associated with subsequent arterial obstruction or arterio-portal shunt, and Lipiodol retention in the portal vein was related to subsequent hepatic lobe atrophy.