In a retrospective study, we tested the hypothesis that anticoagulant therapy with warfarin sodium (Coumadin) has a beneficial influence on the long-term prognosis in patients with primary pulmonary hypertension (PPH) and aminorex-induced plexogenic pulmonary hypertension. The study included a total of 173 patients from two European cities. One hundred four of these patients took the anorectic drug aminorex (Menocil), which was available in some European countries almost 30 years ago; 69 patients had pulmonary hypertension of unexplained etiology, ie, PPH. Fifty-six of the 104 aminorex-treated patients and 24 patients in the PPH group received warfarin after diagnosis was established. For analysis, patients were divided into four groups according to their history of aminorex intake and anticoagulant therapy. Survival time, changes in hemodynamics (pulmonary arterial pressure), and improvement in quality of life (scored by the New York Heart Association [NYHA] classification) were compared and analyzed. We found that aminorex-treated patients had a better long-term prognosis than those with PPH (7.5 vs 3.9 years; p<0.001). The best mean survival time of 8.3 years was found in anticoagulated aminorex-treated patients, compared to 6.1 years in nonanticoagulated aminorex-treated patients. Moreover, aminorex-treated patients who received anticoagulant therapy soon after the onset of symptoms showed significantly better prognosis (10.9 years) than those who commenced treatment 2 years thereafter (5.9 years) (p≤0.05). In patients with PPH, systolic pulmonary pressure was shown to influence survival time significantly (p≤0.0005); however, this correlation was not found in aminorex-treated patients. An improvement of symptoms like dyspnea on exertion was seen in 44.8% of the anticoagulated aminorex-treated patients, while deterioration was evident in 72.2% of the nonanticoagulated aminorex-treated patients. In conclusion, our study has shown that anticoagulant therapy had a positive influence on long-term survival and a significant improvement in quality of life in patients with PPH, in particular in patients with a history of anorectic drug intake.