Thrombosis is one of the major complications of malignant disease, but the underlying molecular and cellular basis remains elusive. A number of hypotheses have been put forth, including the expression of tissue factor by tumor cells, release of tissue factor during cell death following chemotherapy, intrinsic unique tumor procoagulants and microparticles. Exploration of a potential role of microparticles in cancer-associated thrombosis indicates that tissue factor microparticles are present in a spectrum of cancer patients known to have a high incidence of thromboembolic complications.