Cancer is a disease largely dependent on neoangiogenesis. Cancer neoangiogenesis is often disordered and abnormal, with evidence of coexisting vascular endothelial dysfunction. A novel method of assessing vascular endothelial function in cancer is via the quantification of circulating endothelial cells (CEC). Unusual in healthy individuals, their presence in elevated numbers often indicates substantial vascular endothelial perturbation. Another interesting cell type is the endothelial progenitor cell (EPC), whose numbers increase in the presence of vascular damage. Recent research suggests that EPCs have an important role in tumor vasculogenesis. Another marker being investigated in the context of vascular dysfunction and coagulopathy is the endothelial microparticle (EMP). Thus, CECs, EPCs and EMPs may represent potentially novel methods for evaluating the vascular status of cancer patients. This review will summarize the current position of CECs, EPCs and EMPs in cell biology terms, with particular emphasis on their relationship to malignant disease.