Steroid responsive biliary strictures in patients fulfilling criteria for primary sclerosing cholangitis (PSC) have been reported. The clinical course and response to therapy in patients with PSC with elevated immunoglobulin G4 (IgG4) levels has not been investigated previously. Patients with PSC were screened for IgG4-related biliary disease during 2006 to 2008 and data were collected prospectively. A total of 33 out of 285 (12%) patients with PSC (18 males) had elevated IgG4 (>140mg/dL) with a median age of 46 years (interquartile range 29-60); 24 could be evaluated. All patients had both intrahepatic and extrahepatic biliary strictures. Pancreatic disorders were found in 4 (17%), and 11 of 24 (46%) presented with jaundice; 8 of 24 (33%) received biliary stenting for a median time of 4 months (0-6). Liver cirrhosis was diagnosed in 12 of the 24 (50%). Overall, 18 patients were treated with corticosteroids and 6 patients managed conservatively. Nine of 10 patients with elevated bilirubin had improvement. Alkaline phosphatase decreased significantly at 2 months and at last follow-up. IgG4 levels at baseline were 242 (216-357) mg/dL and decreased to 109 (80-236) at 2 months (P < 0.05) and 174 (115-269) at last follow-up (P < 0.05). A total of 39% had adverse effects of steroids, mostly hyperglycemia. Relapses occurred in 7 of the 14 (50%), but biliary stents could be removed in all. Elevated IgG4 levels were observed in 12% of typical patients with PSC. Prevalence of cirrhosis was high, suggesting a severe liver disease course. Most patients had a good biochemical response to steroids, but adverse effects were common. Future work should be directed at finding therapy that is more effective, better tolerated, and of more lasting benefit.