Researchers at the Center for Disease Control looked at the number of cases of blood clots among hospital patients in the U.S. from 2007-09.
They found an annual estimated average of more than 547,000 cases.
Venous thromboemolism consists of deep vein thrombosis and pulmonary embolisms.
This study found the older the patient the greater the risk.
Authors say the findings emphasize the need to increase awareness and prevention about dangerous blood clots.