Purpose: To analyze the enhancement patterns and morphology of peripheral cholangiocarcinomas (CCs), as seen on three-phase helical CT.Materials and Methods: Three-phase helical CT scans of 25 cases of 24 patients with pathologically-proven CCs were retrospectively reviewed. After intravenous administration of contrast media, scans of the hepatic arterial phase(HAP) were obtained at 30 seconds, of the portal venous phase(PVP) at 70 seconds, and of the delayed phase(DP) at 3 minutes.Results: Linear, dense, marginal enhancement was seen in 17 CCs (68%), mainly on HAP images (64%) while thick, band-like, peripheral enhancement was seen in 18 (72%), on either PVP(52%) or DP(44%). Internal enhancement was observed in 23 CCS(92%) on PVP(68%) and/or DP(88%), and 19 CCs(76%) among them showed incomplete enhancement of stippled and/or septated patters. Most (76%) were seen throughout all three phases to be hypoattenuating, as compared to the surrounding parenchyma. On HAP, wedge-shaped parenchymal enhancement was demonstrated at the periphery of 19 CCs (76%) suggesting impaired portal flow. Associated morphologic findings were satellate nodules(n=15, 60%), lymphadenopathy(n=14, 56%), focal dilatation of intrahepatic ducts around the tumor (44%), umbilication of the liver surface (50%), and clonorchiasis (44%).Conclusion: On three-phase helical CT, peripheral cholangiocarcinoma showed linear marginal enhancement on HAP, thick peripheral enhancement on PVP and/or DP, stippled and septated enhancing foci on DP, and peritumoral wedge enhancement on HAP. Associated findings such as satellite nodules, focal dilatation of the intrahepatic ducts, umbilication of the tumor, and clonorchiasis were helpful.