PURPOSE: Arterial enhancement of intrahepatic cholangiocarcinoma (ICC) has been noted. To precisely identify the characteristics of tumor enhancement patterns, we examined the relationship between CT attenuation in the tumor and clinicopathological parameters or prognosis. METHODS: Subjects were 42 ICC patients who had undergone hepatectomy. microvessel density (MVD) determined by CD34 staining was compared with imaging. Attenuation was calculated in images from multidetector CT of tumor and non-tumorous regions. Enhancement patterns were divided into two groups: arterial enhancement with higher attenuation (>16 HU; Hyper group, n = 12); and arterial enhancement with lower attenuation (Hypo group, n = 30). RESULTS: Univariate analysis identified high tumor marker level, increased size, less-differentiation, incomplete resection, increased bleeding, and lower MVD as significantly associated with poor survival (p < 0.05). Increased attenuation throughout the whole ICC correlated significantly with radiological findings and MVD. Concomitant hepatitis, well-differentiation, and smaller tumor were more significantly frequent in the Hyper group than in the Hypo group (p < 0.05). Postoperative early recurrence was significantly less frequent in the Hyper group, and overall survival was significantly better in the Hyper group (p < 0.05). CONCLUSIONS: Increased CT attenuation correlated with ICC tumor vascularity. Increased tumor enhancement in the arterial phase was associated with chronic hepatitis, lower malignancy, and better survival.