Objectives: Our purpose was to evaluate the associationbetween idiopathic pulmonary arterial hypertension (PAH)and obesity, as indicated by the body-mass index (BMI), interms of the all-cause mortality in a group of patients froma specialized center.Materials and Methods: In this study, we retrospectivelyanalyzed 78 consecutive adult patients with idiopathic PAH.The patients were classified into two groups as the deceased(D) and the survived (S). A set of data was collected for eachpatient, including gender, age, weight, height, BMI (kg/m2),World Health Organization functional class (WHO FC),brain natriuretic peptide (BNP), hemoglobin, the presence ofatrial fibrillation (AF), 6-minute walking distance (6MWD),echocardiographic and hemodynamic parameters.Results: The mean follow-up period was 33.7 months(maximum: 128 months), 38 deaths (48.7%) were noted.The two groups were found to be similar in terms ofgender, age, and the presence of AF. The median BNPlevel in group D was significantly higher than that in groupS (p<0.001). Baseline WHO FC III-IV was significantlymore common in group D than that in group S (89.5% vs57.5%, p=0.003). Group D had significantly lower BMIand 6MWD compared to those in group S (p<0.001 andp=0.017, respectively). Multivariate logistic regressionanalysis showed that BMI [Odds ratio (OR)=0.632, 95%confidence interval (CI)=0.478-0.837, p=0.001] and6MWD (OR=0.981, 95% CI=0.970-0.993, p=0.002)were independent predictors of mortality in this cohort.The receiver operating characteristic curve analysis wasperformed to assess the utility of BMI as a predictor ofmortality. The optimal BMI cut-off was 24.25 kg/m2,with 60.5% sensitivity and 82.5% specificity (area underthe curve=0.759, 95% CI=0.654-0.864, p<0.001) and thepatients with a BMI of ≤24.25 had worse prognosis basedon the Kaplan Meier analysis survival curves (log-rankp<0.004).Conclusion: BMI seems to be linearly but inversely relatedto all-cause mortality among patients with idiopathic PAH.