The past decade has seen increased application of 18-flurodeoxyglucose positron emission tomography (18FDG-PET) imaging to help diagnose and monitor disease, particularly in oncology, vasculitis and atherosclerosis. Disordered glycolytic metabolism and infiltration of plexiform lesions by inflammatory cells has been described in idiopathic pulmonary arterial hypertension (IPAH). We hypothesized that increased 18FDG uptake may be present in the lungs, large pulmonary arteries and right ventricle of patients with pulmonary hypertension, and that this uptake would be related to markers of immune activation. We imaged the thorax of 14 patients with pulmonary hypertension (idiopathic and chronic thromboembolic) and six controls by 18FDG-PET/computed tomography (CT) and measured uptake in the lung parenchyma, large pulmonary arteries and right ventricle. 18FDG uptake in the lungs and pulmonary arteries was normalized for venous blood activity to give a target-to-background ratio (TBR). Blood was contemporaneously drawn for high-sensitivity CRP – C-reactive protein (CRP) (hsCRP), N-Terminal Probrain natriuteric peptide (NT-ProBNP) and other inflammatory cytokines. IPAH patients had significantly higher lung parenchymal TBR (P =0.034) and right ventricle FDG uptake (P=0.007) than controls. Uptake in the main pulmonary arteries was similar in chronic thromboembolic pulmonary hypertension, IPAH and controls. There were no correlations between 18FDG uptake and hsCRP or inflammatory cytokine levels. NT-ProBNP correlated with RV uptake in those with pulmonary hypertension (r=0.55, P =0.04). In this pilot study, we found increased 18FDG uptake in the lung parenchyma and right ventricle of subjects with IPAH. The lung uptake might be useful as a surrogate marker of increased cellular metabolism and immune activation as underlying mechanisms in this disease. Further evaluation of the impact of targeted therapies in treatment-naïve patients and the significance of right ventricular uptake is suggested.