Fever patterns associated with pulmonary thromboembolism have not been well characterized. Upon review of 35 consecutive patients with angiographically documented pulmonary emboli, fever was present in 24 patients; and in 20, it was attributed solely to pulmonary thromboembolism. Analysis of these cases indicates that high fever (temperature greater than 39 degrees C) due to pulmonary thromboembolism may occur early, and low-grade fever may continue for a week or more. Fever persisting beyond six days, however, especially with temperatures over 38.5 degrees C, should not be ascribed to pulmonary thromboembolism unless other causes have been carefully excluded. If the clinical setting and patient's findings are consistent with pulmonary thromboembolism, one should not be deterred from presumptively making this diagnosis and initiating therapy because of the presence of high fever.