After the Great East-Japan Earthquake, the prevalence of deep vein thrombosis (DV T) in disaster shelters in Ishinomaki (Pacific coast, Miyagi, Japan) was found much higher than that ever reported in Japan. In Ishinomaki, twelve patients were found to have pulmonary thromboembolism for one month since the earthquake and DV T was found in 10 of those patients. The calf DV T was examined using ultrasonography in the shelters (from March to July 2011) and in temporary emergency housings (from August to December 2011). Calf DV T was found in 190 of 701 evacuees. DV T prevalence was higher in the tsunami-flooded shelters (34.2%) than in that in the non-flooded shelters (19.1%). This indicated that deteriorated and crowded condition in the tsunami-flooded shelters might induce thrombogenesis in calf veins. Therefore, evacuees were recommended to leave tsunami-flooded areas. DV T prevalence in the shelters was gradually reduced, however, that was still higher in the temporary emergency housings (8.9%) than in the non-disaster area in Japan (2.2% in Yokohama city). The risk of calf DV T in the temporary emergency housings was increased because of reduced blood flow in the calf veins caused by immobility. The residents of the housings were required to be physically active to avoid calf DV T. (English translation of Jpn J Phlebol 2013; 24: 380–384)