To test whether the clinical presentation and prognosis of fenfluramine-induced pulmonary hypertension (PH) differs from primary PH (PPH), we compared the clinical profile and outcome of 10 patients with fenfluramine-induced PH with that of 70 patients with PPH referred to our center over the same time frame and treated identically. Patients with diet pill PH were similar to those with PPH with respect to hemodynamics. However, patients with fenfluramine-induced PH had poorer survival: 1-year survival 50% versus 88%, and 3-year survival 17% versus 60%.