Pulmonary hypertension is diagnosed by various investigations that are essential for making the diagnosis. Following a careful history and physical examination, an electrocardiogram, a chest X-ray, lung function studies, blood tests and an echocardiogram form the basis of the diagnostic algorithm. Following these studies, a right and sometimes additional left heart catheterization are carried out to establish the diagnosis and to perform acute vasodilator testing. Most of these studies are performed at rest. However, exercise studies are an important part of the functional assessment in this group of patients. Exercise capacity can be estimated by functional class, measured with the 6-min walk test or comprehensively assessed by cardiopulmonary exercise testing with gas exchange analysis. Once the diagnosis and etiology of pulmonary hypertension have been established, several parameters can predict outcome in these patients: functional class, right ventricular function, pulmonary hemodynamics, and certain laboratory parameters (uric acid, brain natriuretic peptide, troponin, endothelin-1). In addition, exercise parameters such as walking distance, peak oxygen uptake or peak systolic blood pressure can reliably predict prognosis in these patients.