The epidemiology of pulmonary arterial hypertension (PAH) has changed over the last decade. Remarkable advances in understanding the pathobiology and clinical care required in PAH have resulted in improved quality of life and survival. Despite such important progress, the long-term rate of survival is still unacceptable. The epidemiology of PAH could not be easily generalized globally, due to the fact that nearly all of the present data has been gathered from Western, multicenter, prospective registries. There are potentially marked differences in PAH patients from Western and Eastern populations, and from developed and developing countries. Therefore, it is clear that more registry data will be needed to address novel questions emerging with improved knowledge of PAH.