Sixty patients with silicosis were examined by right heart catheterization and lung function tests during 1958-1966. In the 12-20 years follow-up the information was received of 57 patients (95%). 38 patients died (66.6%), 26 of them of the sequelae of silicosis. The death rate and the length of survival are related to mean pulmonary artery pressure, pressure gradient across pulmonary vascular bed, pulmonary vascular bed, pulmonary vascular resistance (PVR), arterial oxygen saturation (SaO2), vital capacity (VC) and forced expiratory volume (FEV). 12-year mortality in patients with pulmonary hypertension at rest was 81.3%, in contrast to 40.2% in the other patients. No patient with PVR higher than 2.55 u. survived. No patients with SaO2 lower than 89% survived 10 years. Patients with VC higher than 4000 ml at the initial examination are still living. By the method of discriminating analysis 2 main factors determining the prognosis were identified: pulmonary artery pressure and FEV 1".