Background: pulmonary thrombo-endarterectomy (PTE) is the treatment of choice for chronic thromboembolic pulmonary hypertension in operable patients. Certain risk factors may be associated with bad outcomes after this surgery. Objective: The aim of the current work was to investigate the effect of delay in having surgery on different outcomes after PTE. Subjects and Methods: This interventional prospective`e and retrospective study included a total of 20 patients who underwent pulmonary thromboendarterectomy (PTE), attending at the Department of cardiothoracic surgery, Cairo University Hospitals. This study was conducted between June 2019 and April 2021.  Results: The more delayed the surgery, the higher the postoperative pulmonary vascular resistance (PVR), patients who had exceeded 13 months since the diagnosis of chronic thromboembolic pulmonary hypertension )CTEPH( significantly developed poor postoperative functional class, patients who underwent surgery more than 16 months after the diagnosis of the disease significantly developed postoperative reperfusion lung injury. Conclusion: It could be concluded that delayed PTE is associated with poor postoperative functional class, higher degree of pulmonary vascular resistance and more incidence of reperfusion lung injury.