Pulmonary arterial hypertension (PAH) is a complex disease with a poor prognosis, which has known in the last years great advances in understanding the pathophysiological mechanisms underlying the characteristic vascular proliferative lesions, thus allowing the development of several specific drugs. Nevertheless, it still presents a high mortality, therefore early diagnosis and prognostic stratification seem to be of paramount importance in order to choose the best therapeutic strategies. Circulating biomarkers have been proposed as potentially noninvasive and objective parameters for diagnosis, prognosis and response to therapy; the molecules evaluated to date (markers of dysfunction/neurohormonal activation, myocardial injury, inflammation/oxidative stress, vascular damage/remodelling, end-organ failure, gene expression) reflect the complex pathophysiology of PAH. However, no one of these shows all the characteristics of the ideal biomarker, thus a multi parameter approach is probably desirable. Moreover, the future direction could be the research of structural proteins specifically expressed in the pathological tissue which act as disease-specific markers.