Background: Pulmonary hypertension has not been described as a predisposing ri sk factor for high-altitude pulmonary edema (HAPE) in children. Previous studie s have shown an association of HAPE with abnormally increased pulmonary vasoreac tivity to hypoxia but generally normal pulmonary artery pressure (PAP) after rec overy. Objective: To describe HAPE of relatively rapid onset and its management in a series of children residing at moderate to high altitudes, all of whom had underlying pulmonary hypertension. Methods and Results: From 1997 to 2003, 30 ch ildren came to our center with high-altitude illness. Of these, 10 children (ag ed 4-18 years; male-female ratio, 8:2) living at moderate to high altitudes (1 610-3050 m) -underwent cardiac catheterization after recovery from HAPE, and all were fou nd to have chronic pulmonary hypertension (mean PAP, 38 ±9 mm Hg; pulmonary vas cular resistance, 8.6 ±2.8 U ×m2). Increases in PAP and pulmonary vascular r esistance to hypoxia (16%oxygen) suggest that these children have a reactive pu lmonary pressor response and hence are susceptible to HAPE. Six of the 10 patien ts had predisposing cardiopulmonary abnormalities, and 5 of these 6 patients did not receive a diagnosis prior to the onset of HAPE. Long-term treatment with c alcium channel blockers, bosentan, sildenafil citrate, and/or oxygen lowered PAP , improved symptoms, and prevented the recurrence ofHAPE. Conclusion: Children l iving at altitude who develop HAPE should undergo screening for diagnosis of und erlying cardiopulmonary abnormalities including pulmonary hypertension. Background: Pulmonary hypertension has not been described as a predisposing ri sk factor for high-altitude pulmonary edema (HAPE) in children. Previous studie s have shown an association of HAPE with abnormally increased pulmonary vasoreac tivity to hypoxia but generally normal pulmonary artery pressure ( PAP) after rec overy. Objective: To describe HAPE of relatively rapid onset and its management in a series of children residing at moderate to high altitudes, all of whom had underlying pulmonary hypertension. Methods and Results: From 1997 to 2003, 30 ch ildren Of these, 10 children (ag ed 4-18 years; male-female ratio, 8: 2) living at moderate to high altitudes (1 610-3050 m) -underwent cardiac catheterization after Recovery from HAPE, and all were fou nd to have have chronic pulmonary hypertension (mean PAP, 38 ± 9 mm Hg; pulmonary vas cular resistance, 8.6 ± 2.8 U × m2). Increases in PAP and pulmonary vascular resistance to hypoxia (16% oxyg suggest that these children have a reactive pu lmonary pressor response and hence are susceptible to HAPE. Six of the 10 patien ts had predisposing cardiopulmonary abnormalities, and 5 of these 6 patients did not receive a diagnosis prior to the onset of HAPE. Long -term treatment with c alcium channel blockers, bosentan, sildenafil citrate, and / or oxygen lowered PAP, improved symptoms, and prevented the recurrence ofHAPE. Conclusion: Children l iving at altitude who develop HAPE next undergo screening for diagnosis of und erlying cardiopulmonary abnormalities including pulmonary hypertension.