PURPOSE: To evaluate contrast enhancement patterns of nodular hepatocellular carcinomas (HCCs) on three-phasespiral CT. MATERIALS AND METHOD: A retrospective analysis of contrast enhancement patterns was performed in 48 patients with HCC. Three-phase dynamic CT images of hepatic arterial dominant phase, portal dominant phase, and delayed phase were obtained at 30, 65, and 360 seconds after the initiation of injection of contrast material, respectively. Iodized-oil CT was performed two weeks after angiography and infusion of iodized-oil. Masses were divided into three groups, according to size ; 1-20 mm (n=34), 21-40 mm (n=26), and over 40 mm (n=19). Contrast enhancement patterns of tumors compared with attenuation of surrounding liver parenchyma, were cheracterized asone of four types, as follows : high, iso, low, and mixed attenuation. RESULTS: Seventy-three of 79 HCC nodules detected on iodized-oil CT (92%) were detected on three-phase spiral CT. In the 1-20 mm group, masses showed high-attenuation in the arterial dominant phase(19/34, 55.9%), and iso-attenuation in the portal dominant phase(16/34, 47.1%) and delayed phase(18/34, 52.9%). In the 21-40mm group, masses showed high-attenuation in the arterial dominant phase(21/26, 80.8%), low-attenuation in the portal dominant phase(13/26, 50%) and delayed phase(21/26, 80.8%). In the over 40 mm group, the masses showed mixed-attenuation in the arterial dominantphase(9/19, 47.4 %), low-attenuation in the portal dominant phase(12/19, 63.2%), and delayed phase(16/19, 84.2%).The most common enhancement pattern was high(arterial dominant)-iso(portal dominant)-iso(delayed) in the 1-20 mmgroup (8/34, 23.5 %), high-low-low in the group 21-40mm (8/26, 30.8%), and mixed-low-low in the over 40mm group(5/19, 26.3%). CONCLUSION: Hepatocellular carcinomas showed variable enhancing patterns according to the size ofthe tumor on three-phase spiral CT. Understanding these enhancing characteristics of HCCs on three-phase spiral CT may be helpful in their diagnosis.