Prior observational studies and several case reports have suggested an association between thyroid dysfunction and pulmonary hypertension. This review was designed to evaluate the prevalence and the pattern of pulmonary vasculature involvement in hyper- and hypothyroidism. We identified original research papers and reviews by going through leading journals that publish basic and clinical research in the fields of pulmonary hypertension, hyperthyroidism and hypothyroidism, by electronically searching the Medline database. We directed special attention to papers published from 1972 to 2003. Our findings indicate the presence of a frequent association between hyperthyroidism and pulmonary hypertension (35% in the largest series of cases) which decrease after achievement of a euthyroid state. A possible explanation includes an influence of thyroid hormones which affect growth and maturation of vascular cells and enhanced catecholamine sensitivity causing pulmonary vasoconstriction. Furthermore, several studies suggest a high prevalence of transient pulmonary hypertension in hypothyroidism (49% in the largest series of cases), in these cases autoimmunity play a key role.