AIMS--To investigate the seasonal incidence of massive pulmonary embolism at necropsy. METHODS--Massive pulmonary embolism was defined as a recent thromboembolus occluding the pulmonary trunk or one or both main pulmonary arteries and constituting the main cause of death. A total of 4289 necropsies carried out at East Birmingham Hospital from 1979 to 1988 was reviewed. The number of subjects with massive pulmonary embolism was noted and the accumulated percentage for each calendar month was calculated. RESULTS--Massive pulmonary embolism was found in 13.02% of necropsies carried out in April; in September and October the percentage rose to 14.29 and 14.19, respectively, after falling to 8.04 and 7.80 in June and July. In January and February the incidence fell again to about 9%. CONCLUSIONS--The incidence of massive pulmonary embolism at East Birmingham Hospital is highest in the spring and autumn. Investigation of the seasonal incidence in arctic and tropical areas would be of interest.