The seasonal variation in the necropsy incidence of significant pulmonary thromboembolism in Hong Kong was investigated. A total of 3446 adult Chinese necropsies carried out in Queen Mary Hospital, Hong Kong, from 1987 to 1992 showed an overall rate of 3.77% for significant pulmonary thromboembolism. The rates for individual months were calculated and compared. The pattern of seasonal variation showed that there are two troughs in early summer (June, July) and early winter (November, December), with rates between 1.6% and 2.4%. The rates in the months for the rest of the year were between 4.0% and 5.5%. The overall pattern was similar to that of the temperate zone although the climate was quite different.