Mutations in the bone morphogenetic protein receptor type 2 (BMPR2) and activin receptor-like kinase 1, both members of the transforming growth factor-β family, have been reported in pulmonary arterial hypertension. The primary aim of the study was to determine the frequency of BMPR2 mutations in 75 children and 66 adults with idiopathic pulmonary arterial hypertension (IPAH). Our secondary aim was to ascertain whether clinical parameters such as thyroid disease and antinuclear antibodies defined the mutation-positive patients. Clinical evaluation consisted of right heart catheterization, evaluation of thyroid function, and serologic determinations of ANAs and specific autoantibodies related to connective tissue diseases. Exonic BMPR2 mutations were determined by nucleic acid sequencing.