PURPOSE: To evaluate the characteristics of contrast enhancement of peripheral cholangiocarcinoma, as seen on spiral CT. MATERIALS AND METHODS: Spiral CT was used to examine twelve patients with peripheral cholangiocarcinoma of the liver. All underwent conventional CT before contrast enhancement. After the administration of contrast material, two-phased spiral CT was used to investigate seven patients, and three-phased spiral CT, to investigate five. In each phase, we analysed the patterns of contrast enhancement at the central and peripheral portions of the lesion, and compared these with the patterns of normal liver parenchyma. We evaluated changes, according to time lapse, in the central low-density area, and obtained the phase-density curve with the cursor placed at the central portion of the lesion. For three-phased spiral CT examinations, we also tried to determine the phase dvring which the margin of the lesion was most clearly demonstrated. RESULTS: During the arterial phase, eight of twelve patients (67%) showed hyperdensity in the peripheral portion of the lesion; during the portal phase, four of five patients (80%) showed hypodensity in both the central and peripheral portions. During the delayed phase, six of twelve patients (50%) showed isodensity and five showed high density in the peripheral portion. Compared to those in the arterial phase, central hypodense areas relative to normal liver parenchyma in the delayed phase decreased in eleven of twelve patients (92%). On phase-density curves, the density of the central portion of the lesion increased progressively in nine of twelve patients (75%). On three-phased CT, the margin of lesion was-in all five patients - most clearly demonstrated in the portal phase. CONCLUSION: On spiral CT, the central portion of peripheral cholangiocarcinoma always showed low density and the peripheral portion showed high, low, or iso or high density, depending on the phase. In addition, spiral CT clearly demonstrated a minimal centripetal pattern of contrast enhancement. We therefore conclude that in the diagnosis of peripheral cholangiocarcinoma, the characteristics of contrast enhancement are helpful.