There is a difference between thrombosis and embolism. Although both thrombosis and embolism cause blockage of blood vessels, causing poor blood flow and resulting in inadequate blood supply or venous return obstruction, there is a fundamental difference between thrombosis and embolism. Thrombus is formed in situ, mostly due to risk factors or hypercoagulable state, local platelet aggregation, abnormal coagulation factors, and formation of thrombus in situ in the target lesion, resulting in vascular blockage. Embolism, on the other hand, is not formed in situ, but rather a thrombus from another site is dislodged and follows the direction of the circulatory system and blood flow to another site, causing a blockage of the vessel. Therefore, once a patient is suspected to be embolized, the source of the embolism should be evaluated to see if a thrombus formed in another site or if there is a tumor embolism, in addition to the vessel at the embolism. Therefore, although the treatment of thrombosis and embolism is much the same, it is also important to clarify their pathological causes and etiology.