Pulmonary thromboembolism (PTE) is caused when thrombi are detached from the deep vein of the lower leg. In the field of forensic medicine, it is a well-known cause of sudden death. It has been reported that risk factors for PTE include surgery, trauma, extensive bed rest, and malignant neoplasm, among others; in addition, long-haul air travel is associated with a slightly increased risk for PTE, though such cases are rare. Recently, PTE had been reported in association with different conditions, such as ethrombosis, seated immobility thromboembolism, driving for long periods, and after traveling. The authors performed autopsies on 3 patients who died suddenly after 3 to 4 days of prayer in a prayer center or hermitage. It was confirmed that all deaths were caused by thrombi that had developed in the deep vein, obstructing the pulmonary artery. It was concluded that during repeated praying activities over an extensive time period, the kneeling position might have caused PTE. It is also possible that dehydration due to fasting may affect the formation of thrombi. According to the literature, PTE cases developed in association with prayer activity and position have not been reported to date, and so PTE caused by prayer activity is thought to be a new type of PTE developed in association with a certain life style. Therefore, people should be advised that a position involving a long period of immobilization, including long periods of prayer, could raise the risk of PTE. In addition, social policies to prevent the development of this kind of PTE are needed.