A 43-year-old woman had two episodes of lung edema at moderate altitudes. She had taken slimming pills containing fenfluramine hydrochloride and diethylpropion hydrochloride. At sea level, catheterization of the right side of the heart showed a mean pulmonary artery pressure of 16 mm Hg, which increased to 34 mm Hg with mild exercise in a supine position. An extensive workup failed to identify a cardiac or a pulmonary cause of pulmonary hypertension. This patient experienced mild primary pulmonary hypertension related to the intake of anorexigens, which was revealed by high-altitude pulmonary edema.