Pulmonary hypertension (PH) associated with lung disease and hypoxia (WHO Group III) is one of the most common forms of pulmonary hypertension. It also encompasses a very diverse group of diseases where the PH is an extremely important determinant of functional limitation and prognosis. In this group of diseases, PH is common in advanced disease, however its prevalence in milder disease is not known. None of the non-invasive screening methods have been found to be accurate and the best screening tool, Doppler echocardiography, is especially prone to error. Treating these patients can be a frustrating experience because of the lack