Pulmonary hypertension (PH) is a syndrome characterized by marked remodeling of the pulmonary vasculature and a progressive increase in the pulmonary vascular load, resulting in right ventricular hypertrophy and remodeling. PH is a serious complex disorder which is associated with high morbidity and mortality rates. It is considered one of the major complications of myeloproliferative neoplasms (MPNs) mainly in advanced disease. It is classified according to the World Health Organization (WHO) into five groups. MPNs are involved within group 5 PH which is due to an unclear and/or multifactorial etiology. The occurrence of PH in MPNs patients has a bad impact on the prognosis of the disease and on the survival in those patients. The pathogenesis of PH in MPNs patients is multi-factorial. Three characteristic clinical types of PH are recognized as unique pathologic mechanisms in MPNs patients: chronic thromboembolic pulmonary hypertension (CTEPH), precapillary pulmonary hypertension, and drug-induced pulmonary hypertension.