The mean pulmonary artery pressure (PAP) was measured in 34 patients with moderate to severe chronic obstructive pulmonary disease (FEV1, 1,010 +/- 460 ml)) and was correlated with the following 3 indexes derived from the chest roentgenogram: (1) the hilar thoracic index, (2) the diameter of the descending branch of the right pulmonary artery, (3) the hilar width, and (4) the cardiothoracic ratio. The mean PAP was 29.0 mm Hg and 20 of 34 patients had an elevated mean PAP (greater than 20 mm Hg). Nineteen of the 20 patients (95%) with an elevated mean PAP had a hilar thoracic index of 36 or above, whereas none of the 14 patients with a normal mean PAP had a hilar thoracic index above 35. Nineteen of the 20 patients (95%) with an elevated mean PAP had diameters of the descending branch of their right pulmonary artery of 20 mm or more compared with only 3 of 14 patients (21%) with a normal mean PAP. The PAP best correlated with the hilar thoracic index (r = 0.74, p less than 0.01) and was significantly correlated with the other 3 indexes. However, the accuracy with which the PAP could be predicted was only +/- 21 mm Hg. We conclude that the chest radiograph is useful in screening patients with COPD for elevated PAP, but that it cannot be used to predict the PAP accurately.