Pulmonary endarterectomy surgery (PEA) offers the possibility of a cure for patients suffering from chronic thromboembolic pulmonary hypertension (CTEPH). Despite growing experience worldwide, the approach and criteria for patient selection remain variable and center- or expert-dependent. A significant proportion of patients with CTEPH may be turned down for PEA for a number of reasons, most frequently over concerns of distal or inaccessible disease. Although traditional preoperative testing and currently available tools are adequate in identifying the presence of proximal disease in CTEPH, they provide only limited information on the status of the microvasculature. Because persistent pulmonary hypertension is the most important determinant of post-PEA outcome, the preoperative identification of patients with CTEPH with concomitant small-vessel disease and/or microvascular disease is crucial. Pulmonary vascular resistance (PVR) is a useful parameter for assessing potential concomitant small-vessel disease. By assessing the relative contribution of small vessels to the PVR, the pulmonary artery occlusion technique represents a promising tool for determining the risk of surgery in patients with high PVR. More information is required regarding the potential value or risk of preoperative medical therapies. Although traditional surgical classification of CTEPH takes place intraoperatively, there is a need for a preoperative classification system and consensus on operability. A preliminary preoperative classification system has been proposed.