PURPOSE: To study the CT patterns of left lobar atrophy, including pathologic and hemodynamic features, incases of primary biliary disease. MATERIALS AND METHODS: CT findings of left hepatic lobar and segmental atrophyin 26 patients with histologically or radiologically-proven underlying bile-duct disease were reviewed. Seventeen cases were oriental cholangiohepatitis (OCH) with left intrahepatic stones and nine were cholangiocarcinomainvolving the hilar or left hepatic bile duct. The distribution and appearance of atrophy and adjacent lobarhypertrophy were studied. CT scans were examined for the presence of stenosis or obstruction of the left portalvein, and the enhancing pattern of lobar atrophy was analysed. In patients who had undergone left lobectomy, themechanism of lobar atrophy was correlated with radiographic and pathologic features. RESULTS: All patients showedbile duct dilatation localized to atrophic left hepatic segments. In cholangiocarcinoma, the distribution ofatrophy was characteristically lobar, in contrast to segmental distribution in OCH. Compensatory hypertrophy wasmore common in OCH and particularly involved the caudate lobe. Organic and functional occlusion of the left portalvein was a cause of atrophy, even in OCH. Periportal fibrosis and inflammation were the main pathological featureof atrophy. On spiral CT scan, delayed enhancement of atrophic liver parenchyma was the characteristic feature. CONCLUSION: Lobar or segmental left hepatic lobe atrophy is seen in bile duct disease caused by OCH orcholangiocarcinoma. This finding suggests that the disease process is advanced, and that there is obstruction ornarrowing of the left portal vein, associated with periportal fibrosis and inflammation.