Primary biliary cirrhosis (PBC)-autoimmune hepatitis (AIH) overlap syndrome is a clinical entity characterized by the occurrence of both conditions at the same time in the same patient. In addition to PBC-AIH overlap syndrome, transitions from one autoimmune disease to another have been reported, but no systematic series have been published. We report a series of 12 patients with consecutive occurrence of PBC and AIH (i.e., PBC followed by AIH). Among 282 PBC patients, 39 were identified who fulfilled criteria for probable or definitive AIH. AIH developed in 12 patients (4.3%). The baseline characteristics of the patients were similar to those of patients with classical PBC. Time elapsed between the diagnosis of PBC and the diagnosis of AIH varied from 6 months to 13 years. Patients with multiple flares of hepatitis at the time of diagnosis of AIH had cirrhosis on liver biopsy. Ten patients were given prednisone +/- azathioprine; short-term as well as sustained remissions were obtained in 8 of these, while two had multiple relapses and eventually died 8 and 7 years after diagnosis of AIH. In conclusion, the development of superimposed AIH could not be predicted from baseline characteristics and initial response to UDCA therapy. If not detected early, superimposed AIH can result in rapid progression toward cirrhosis and liver failure in PBC patients.