Idiopathic pulmonary fibrosis (IPF) is a progressive clinical syndrome of unknown etiology and fatal outcome. Currently available therapies are ineffective and associated with significant adverse effects. Pirfenidone, a new, investigational antifibrotic agent, was evaluated for its tolerability and usefulness in terminally ill patients with advanced IPF. Consecutive patients with IPF and deterioration despite conventional therapy or who were unable to tolerate or unwilling to try conventional therapy were treated with oral pirfenidone. Treatment was administered on a compassionate basis (open-label). Fifty-four patients were followed for mortality, change in lung function, and adverse effects. Their mean age was 62, mean duration of symptoms 4.6 yr, and time since lung biopsy was 3.2 yr. Conventional therapy was discontinued in 38 of 46 patients; the other eight were able to decrease their prednisone dosage and eight had no previous conventional treatment. One- and 2-yr survival was 78% (95% CI 66%, 89%) and 63% (95% CI 50%, 76%), respectively. Patients whose lung functions had deteriorated prior to enrollment appeared to stabilize after beginning treatment. Adverse effects were relatively minor. The results of this study are encouraging. Pirfenidone is a promising new treatment for IPF that is well tolerated.