Cancer is frequently complicated by thrombosis, which may even be the first sign of an unrecognized cancer. There are several risk factors for cancer-associated thrombosis, such as type of malignancy, the presence of metastatic disease, and the use of chemotherapy. In most patients with cancer, a procoagulant state can be identified, ranging from subclinical laboratory abnormalities to full-blown disseminated intravascular coagulation. A specific entity is the occurrence of thrombotic microangiopathy that is specifically related to (high-dose) chemotherapy and radiotherapy. The pathogenetic pathways that play a role in the cancer-associated coagulopathy have been identified in recent years.