To assess the value of CT in chronic pulmonary embolism (CPE), CT scans and pulmonary angiograms of 21 consecutive patients were reviewed. Computed tomography was better than angiography in assessing proximal clots (three thrombi not seen by angiography, three angiographic false-positives confirmed by surgery). Furthermore, CT was able to analyze pulmonary arteries distal to angiographic amputations. Computed tomography was less sensitive than angiography for vascular distortions (38 vs. 50%) and stenosis (35 vs. 71.8%). Pulmonary infarctions were better detected and characterized by CT than by angiography. Isolated parenchymal ground-glass opacities were seen by CT in 18 patients, especially in those with right cardiomegaly. High resolution CT delineated them better than did standard CT. Computed tomography may be a useful adjunct to angiography in the assessment of CPE.