Purpose This study aimed to investigate the efficacy of ursodeoxycholic acid (UDCA) for Japanese patients with autoimmune hepatitis (AIH). Methods One hundred forty-seven patients were investigated. Results As initial treatment, 25 patients received UDCA (300-600 mg/day) monotherapy (UDCA group), 40 received a combination of prednisolone (PSL) (C20 mg/ day) and UDCA (combination group), 68 received PSL monotherapy (PSL group), and 14 received other treatments. During the follow-up, in the UDCA group, PSL was added to 8 of 12 patients failing to achieve the normalization of serum transaminase levels with UDCA monotherapy. Cumulative incidence of the normalization of serum transaminase levels was 64% in the UDCA group, 95% in the combination group, and 94% in the PSL group (log-rank test, P = 0.0001). UDCA group required longest periods until the normalization of serum transaminase levels. Eleven patients, who achieved persistent normalization Y. Miyake (&) Á F. Ikeda Department of Molecular Hepatology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan e-mail: miyakeyasuhiro@hotmail.com F. Ikeda e-mail: fikeda@md.okayama-u.ac.jp -009-9155-9 of serum transaminase levels with UDCA monotherapy, did not reach liver failure or develop hepatocellular carcinoma for 49.7 (range = 13.4-137.3) months. Meanwhile, during the taper of PSL, doses of PSL at the initial relapse were lower in patients treated with PSL and UDCA than in those treated with PSL monotherapy, and initial relapse occurred earlier in patients treated with PSL monotherapy. Conclusions UDCA monotherapy is effective for some Japanese AIH patients; however, UDCA monotherapy for patients with either high-grade inflammatory activity or poor residual capacity of liver function is not recommended because they may reach liver failure before achievement of remission. Meanwhile, additional use of UDCA during the taper of corticosteroids may be effective for the prevention of early relapse.123 Hepatol Int (2009) 3:556-562 DOI 10.1007/s12072