Kim NH, Hemnes AR, Chakinala MM, et al. - To report clinical features, results, as well as dosing/titration regimens of patients managed with selexipag [a selective oral prostacyclin-receptor agonist indicated for pulmonary arterial hypertension (PAH) treatment] in routine clinical practice, a US-based, ongoing, multicenter, prospective observational study (target N = 800) named SPHERE (SelexiPag: tHe usErs dRug rEgistry) is gathering data from selexipag-treated patients in real-world clinical practice. Experts herein report on the first 500 patients enrolled. In most patients, selexipag was started >60 days prior to enrollment. At initiation, the presence of WHO functional class (FC) II disease, WHO functional class (FC) II or III disease was evident in 31.0% and in 49.6% of patients, respectively. Risk scores continued to be stable in ∼55% and improved in ∼20% of patients at the close of the study. A dose of 1200 µg twice daily (interquartile range: 800–1600 µg twice daily) was the median selexipag maintenance dose. Overall, WHO FC II/III disease was typically present as well as an intermediate risk was evident, despite receiving PAH-specific treatment, in real-world, US-based PAH patients initiating selexipag. In most patients, selexipag was prescribed as a component of a combination regimen. No unexpected adverse effects were found.