The pulmonary artery pressure of 47 patients was compared with radiological criteria of pulmonary hypertension: in rest and exercise. The diameter of the truncus intermediul is the only measurable criterium. A diameter larger than or equal to 18 mm is an indication for latent or manifest cor pulmonale. If the diameter is less than or equal to 15 mm a pulmonary hypertension is improbably. Additional findings (primary pulmonary disease, diameter of the truncus pulmonalis, loss of lung vessel structure in the periphery, marked reduction in vessel caliber--graded 0-3) leads to the diagnosis of manifest cor pulmonale on the basis of routine x-ray of the chest. The differentiation between manifest and latent cor pulmonale ist possible in most cases. An overestimation of the primary lung disease, particularly by fibrosis, may mistead from the correct diagnosis.