The prompt and accurate recognition of non-malignant complications is of critical importance in the care of cancer patients. Pulmonary thromboembolism is particularly important because it is common, treatable and frequently difficult to diagnose. Two patients are presented who died of recurrent pulmonary thromboemboli which were unrecognized because open lung biopsies showed diffused interstitial pneumonitis. The association of pulmonary thromboembolism and interstitial inflammation has been recognized at autopsy, and there are a number of plausible mechanisms which could link these processes. Interstitial pneumonitis should be added to the numerous protean manifestations with which pulmonary thromboembolism is associated.