This report describes a 28-yr-old patient with pulmonary veno-occlusive disease (PVOD). She presented with pulmonary hypertension, hypoxemia, and interstitial pneumonitis. We report the discordance between the response of her hypoxemia and interstitial pneumonitis, which resolved with corticosteroid therapy, and her progressive pulmonary hypertension, which caused fatal right heart failure. This report emphasizes that the radiographic interstitial shadowing of PVOD may be caused by either (1) an inflammatory interstitial pneumonitis (which may be responsive to anti-inflammatory therapy) or (2) interstitial pulmonary edema, or both.