Idiopathic pulmonary fibrosis (IPF) was found to have a higher incidence than previously assumed and the population involved was younger. These findings were made in a retrospective investigation during the period 1986-1990. The condition should be suspected on the basis of the radiographic characteristics, reduced lung volume (TLC), decreased DLco during testing of pulmonary function, hypoxemia at rest and also the symptoms revealed in the medical history. It is of importance for planning of treatment that the diagnosis of IPF is confirmed early by excision biopsy of pulmonary tissue. Patients with IPF were treated successfully by intravenous administration of a solution of 500 mg methylprednisolone in 500 ml isotonic glucose. This regime is administered for three consecutive days and supplemented by azathioprine as required. In order to prevent further progression of this chronic disease, patients with IPF should be followed-up at frequent intervals.