BACKGROUND: The coexistence of primary biliary cirrhosis (PBC) and autoimmune hepatitis (AIH) has been called "overlap syndrome," but diagnosis is challenging and the natural history of this syndrome has not been demonstrated. The importance of the diagnosis of PBC-AIH overlap is due to potential therapeutic options. Patients with PBC should receive ursodeoxycholic acid (UDCA); the role of and response to additional immunosuppressive therapy are unknown when AIH overlaps PBC. METHODS AND RESULTS: We reviewed 135 patients with PBC according to a revised scoring system proposed by the International Autoimmune Hepatitis Group (IAHG). Twenty-six patients had features of PBC-AIH overlap and 109 did not. Mean follow-up was 6.1 yr for overlap syndrome patients and 5.4 yr in PBC patients. There was a higher rate of portal hypertension (P=0.01), esophageal varices (P<0.01), gastrointestinal (GI) bleeding (P=0.02), ascites (P<0.01), and death and/or orthotopic liver transplantation (OLT) (P<0.05) in the overlap group. CONCLUSION: In conclusion, esophageal varices, GI bleeding, ascites, and death and/or OLT were more common in the overlap group. The higher risk of symptomatic portal hypertension and worse outcomes in patients with PBC overlap syndrome may justify the risks of immunosuppressive therapy. Large randomized studies are necessary to establish optimal therapeutic strategies.