Abstract Background: Pulmonary arterial hypertension (PAH) is a vascular disease characterised by restricted flow and high pressure through the pulmonary arteries, leading to progressive right heart failure and death. This study reports the global burden of PAH, leveraging all available data and using methodology of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) to understand the epidemiology of this under-researched and morbid disease. Methods: Prior to the current effort, the burden of PAH was included in GBD as a non-specific contributor to "other cardiovascular and circulatory disease" burden. In this study, PAH was distinguished as its own cause of death and disability in GBD, producing comparable and consistent estimates of PAH burden. We used epidemiological and vital registry data to estimate the non-fatal and fatal burden of PAH in 204 countries and territories from 1990 to 2021 using standard GBD modelling approaches. We specifically focused on PAH (group 1 pulmonary hypertension), and did not include pulmonary hypertension groups 2-5. Findings: In 2021, there were an estimated 192 000 (95% uncertainty interval [UI] 155 000-236 000) prevalent cases of PAH globally. Of these, 119 000 (95 900-146 000) were in females (62%) and 73 100 (58 900-89 600) in males (38%). The age-standardised prevalence was 2·28 cases per 100 000 population (95% UI 1·85-2·80). Prevalence increased with age such that the highest prevalence was among individuals aged 75-79 years. In 2021, there were 22 000 deaths (18 200-25 400) attributed to PAH globally, with an age-standardised mortality rate of 0·27 deaths from PAH per 100 000 population (0·23-0·32). The burden of disease appears to be improving over time (38·2% improvement in age-standardised years of life lost [YLLs] in 2021 relative to 1990). YLLs attributed to PAH were similar to estimates for conditions such as chronic myeloid leukaemia, multiple sclerosis, and Crohn's disease. Interpretation: PAH is a rare but fatal disease that accounts for a considerable health-associated burden worldwide. PAH is disproportionally diagnosed among females and older adults.