Chronic lung disease (CLD) is often complicated by chronic pulmonary vascular changes and pulmonary hypertension (PH) in young children. Current therapies for severe PH in such patients, including oxygen, inhaled nitric oxide, and parenteral prostacyclin, are often suboptimal, cumbersome, and expensive. Recently, oral endothelin receptor blockers and phosphodiesterase-5 inhibitors have been used successfully to control and reverse pulmonary vascular disease in idiopathic PH, but the use and efficacy of these agents in pediatric CLD have not been previously reported. We report a series of six children with CLD and severe PH treated with bosentan (six of six) and sildenafil (four of six). Vascular reactivity was assessed by cardiac catheterization prior to and after 6 months of therapy. Serial echocardiography was also used to assess response. Patients have been treated for 2.1-2.9 years (mean, 2.53 years). Response to therapy has included improvement in oxygenation, symptoms, echocardiographic parameters, and hemodynamics by cardiac catheterization. Transiently elevated liver enzymes were noted associated with viral respiratory infections in two subjects; no other adverse effects were noted. Three patients with large cardiac right-to-left shunts prior to therapy had subsequent shunt reversal, two of whom underwent shunt closure later. Oral therapy with bosentan alone or in combination with sildenafil improves PH in patients with CLD over a period of 3-4 years.