A link between hyperthyroidism and pulmonary hypertension has been reported, but the underlying mechanisms of these two conditions have not been clearly identified. The aim of this study was to determine the clinical correlates of pulmonary hypertension in patients with Graves' disease. Among 50 consecutive patients with Graves' disease referred for echocardiography, 18 patients (36 %) had pulmonary hypertension measured by continuous-wave Doppler echocardiography (pulmonary artery systolic pressure >35 mmHg). The patients with pulmonary hypertension had significantly higher pulmonary vascular resistance (PVR), cardiac output and thyroid-stimulating hormone receptor antibody (TRAb) compared to those without (p < 0.001, p = 0.028 and p < 0.001, respectively). Pulmonary artery systolic pressure had a good correlation with TRAb (r = 0.74, p < 0.001), but was not related to free T4 (r = 0.12, p = 0.419) and free T3 (r = 0.22, p = 0.126). To determine the important variables present in patients with Graves' disease that may be related to pulmonary artery systolic pressure, 4 variables (PVR, cardiac output, TRAb and free T3) were used in the multivariate analysis. In addition to PVR (standard regression coefficient = 0.831, p < 0.001) and cardiac output (standard regression coefficient = 0.592, p < 0.001), TRAb (standard regression coefficient = 0.178, p < 0.001) emerged as a significant variable related to pulmonary artery systolic pressure. Thus, in addition to the effect of thyroid hormone on the cardiovascular system, autoimmune-mediated pulmonary vascular remodeling may play a role in Graves' disease-linked elevated pulmonary artery systolic pressure.