Myeloproliferative neoplasms (MPNs) and myelodisplastic syndromes (MDs) are clonal disorders caused by mutations of myeloid stem cells. Among MPNs, polycythemia vera and essential thrombocythemia are relatively benign disorders in which arterial and venous thromboses represent the main cause of morbidity and mortality. The natural history of MDs is often complicated by both thromboses and haemorrhages, mainly due to platelet quantitative and quantitative anomalies, as well as to treatment complications. In this short review, we focus the attention on the main aspects of thrombophilia in both disorders.