With a quickly growing range of therapeutic options precise prognostic stratification became particularly important for clinical decision making in patients with pulmonary arterial hypertension (PAH). Assessment of disease-specific functional class remains the simplest method and is a fairly reliable way of assessing severity of PAH, and current guidelines recommend a therapeutic algorithm based on functional class evaluation. Six-minute walk is the most widely used test assessing exercise tolerance both in clinical practice and in clinical trials testing new therapies in PAH. Right heart catheterization with a vasoreactivity test is mandatory to identify a subgroup that has good long-term prognosis when treated with calcium channel blockers alone. Echocardiographic variables of documented prognostic value in PAH are not those directly correlated with pulmonary arterial pressure (PAP). Instead, the presence of pericardial effusion, enlarged right atrium, and elevated Doppler index of right ventricular performance have been the most consistently reported signs of poor prognosis. Low or decreasing brain natriuretic peptide (BNP) suggests a good outcome whereas troponin T leak persisting despite therapy is a poor prognostic sign. Biomarkers seem particularly useful for noninvasive follow-up of patients with PAH, and due to simplicity and low costs may successfully compete with echocardiography.