The semiquantitative histopathological analysis of the liver biopsies obtained before and after 4 years of ursodeoxycholic acid (UDCA) therapy in a cohort of primary biliary cirrhosis (PBC) patients is reported. The relationships between elementary histological lesions before treatment and their progression under therapy were assessed. At baseline, two independent groups of lesions, each of which participate in the development of fibrosis, were individualized, i.e., florid bile duct lesions and ductopenia on one hand and lymphocytic piecemeal necrosis, ductular proliferation, and lobular necroinflammatory changes on the other hand. Four years of UDCA therapy were associated with a significant decrease in the prevalence of florid interlobular bile duct (ILBD) lesions, of epithelioid granuloma (P <.001) without any aggravation in the severity of bile duct paucity. Lobular inflammation and necrosis markedly improved (P <.001) whereas the degree of severity of the lymphocytic piecemeal necrosis and ductular proliferation at entry and at 4 years were similar. Worsening of fibrosis was observed in 14 patients (12 of them had a one grade progression) whereas stabilization was noted in 30 of the remaining patients. Severity of both the lymphocytic piecemeal necrosis and lobular inflammation and necrosis at entry was significantly associated with the progression of fibrosis. The results suggest that UDCA therapy influences the process leading to bile duct destruction. Patients with severe lymphocytic piecemeal necrosis and lobular inflammation may need additional therapeutic intervention because they have increased risk of fibrosis progression.