Glucose metabolism measurement using 2-deoxy-2-[18F]-fluoro-D-glucose (18FDG) positron emission tomography (PET) could provide in vivo information about pulmonary vascular remodeling. The purpose of this study was to assess whether pulmonary 18FDG uptake in idiopathic pulmonary arterial hypertension (IPAH) patients changes and, if so, to determine whether the change is related to disease severity and survival. Sixteen IPAH patients who were treated with IPAH-specific therapy and 7 patients who had a myocardial infarction (MI) without pulmonary hypertension were included. IPAH disease severity was determined using the 6-minute walk test and right heart catheterization 2 days before 18FDG PET. Regions of interest were defined for left and right lungs, and standardized uptake values (SUVs), normalized to body weight, injected dose, and plasma glucose level, were derived. Mean SUVs for IPAH left and right lungs were 0.40 ± 0.26 and 0.44 ± 0.18 (P = 0.32), respectively. In MI patients, SUVs were 0.38 ± 0.13 and 0.35 ± 0.10 (P = 0.24) in left and right lungs, respectively. Total lung SUVs were similar in IPAH and MI patients (0.41 ± 0.19 vs. 0.37 ± 0.11; P = 0.56). There was no correlation between SUV and IPAH disease severity parameters. In addition, lung SUV did not predict survival in IPAH patients (hazard ratio, 1.155; 95% confidence interval, 0.16–8.26; P = 0.88). In conclusion, pulmonary 18FDG uptake in treated IPAH patients is low and is not associated with disease severity and survival, thereby limiting its clinical use in patient care.