A prospective study was performed in our center on 60% (n = 36) of patients with systemic lupus erythematosus (SLE) to determine the prevalence and severity of pulmonary hypertension. Twenty-six healthy subjects of similar age and sex served as controls. Pulmonary artery systolic pressure was calculated from the sum of the peak tricuspid insufficiency Doppler pressure gradient and an estimate of right atrial pressure based on inferior vena cava size and its degree of inspiratory collapse. Five patients with SLE (14%) had pulmonary hypertension, defined as pulmonary artery systolic pressure greater than 30 mm Hg. Cardiac indices determined by planimetry of biplane apical 2-dimensional echocardiographic images were low or normal in the patients with pulmonary hypertension implying increased pulmonary vascular resistance as the etiology for elevated pulmonary artery pressure. The mean pulmonary artery systolic pressure in patients with SLE was 25 +/- 10 mm Hg vs 20 +/- 2 in controls (p = 0.002). No control had a pulmonary artery systolic pressure greater than 23 mm Hg. Patients with pulmonary hypertension had a shorter duration of SLE and steroid therapy and a higher prevalence of cytotoxic treatment and Raynaud's phenomenon in comparison to those with normal pulmonary artery pressures. The prevalence of systemic hypertension, interstitial lung disease, pleurisy, pericarditis, cutaneous manifestations, arthritis, renal disease, central nervous system involvement, and hematologic abnormalities was similar in patients with SLE with normal and elevated pulmonary artery pressure. Our study suggests that pulmonary hypertension in SLE is common but usually mild.