Our aim was to evaluate the safety and assess the efficacy of pirfenidone, an antifibrotic drug, in patients with primary sclerosing cholangitis (PSC). Twenty-four patients with PSC were enrolled in this pilot study. Oral pirfenidone, 2400 mg daily, was given for one year. Liver biochemistries were determined at three-month intervals. The Mayo risk score was calculated, and liver biopsy and endoscopic cholangiography were performed at entry and at one year of treatment. No significant changes in liver biochemistries were noted at the end of the treatment period or at any of the three-month intervals. The Mayo risk score did not change significantly, and no significant changes were noted in the degree of inflammation, fibrosis, histologic stage of disease, or cholangiographic findings at the end of the treatment period. Adverse events occurred in 20/24 (83%) patients, but disappeared shortly after pirfenidone was discontinued. Pirfenidone did not benefit patients with PSC, and it was frequently associated with adverse events. The results of this pilot study discourage further trials of pirfenidone in patients with PSC.