PURPOSE: To evaluate the triple-phase helical CT findings of adenomatous hyperplasia of the liver. MATERIALS AND METHODS: Forty-seven cases of adenomatous hyperplasias (size range: 8 -45 mm, mean: 14mm) in nineteen patients were confirmed by histologic examination following surgery (n=32) or gun biopsy (n=15) and formed the basis of this study. All patients underwent helical CT scanning involving the injection of 100mL nonionic contrast material at a rate of 3mL/sec. Hepatic arterial, portal venous, and equilibrium phase CT images were obtained 30, 60, and 180 seconds, respectively, after the start of contrast injection. The attenuation of each nodule (hyper-, iso-, hypo-, or mixed) was retrospectively determined and the detection rate according to lesion size (> or =14mm or <14mm) was evaluated. RESULTS: Nodule attenuation during the hepatic arterial phase was iso- in 31 nodules, hypo-in nine, hyper-in five, and mixed in two. The results obtained for the portal venous phase were iso-attenuation in 34 nodules,hypo-attenuation in ten, hyper-attenuation in one, and mixed in two. During the equilibrium phase, attenuation was iso-in 34 nodules and hypo-in 13. Triple-phase helical CT detected 18 nodules (38 %); the detection rate was 8 % (2/26) in the small size group(> or =14mm) and 76 % (16/21) in the large size group(< 14mm). This rate was thus significantly higher in the large size group than in that in which lesions were small. CONCLUSION: Triple -phase helical CT revealed that in cases of adenomatous hyperplasia, attenuation was variable,with iso-attenuation the most frequent type. Seventy-six percent of nodules larger than 14 mm were detected. Adenomatous hyperplasia may be seen during the hepatic arterial phase as a hyper-attenuated nodule.