Introduction: Pulmonary thromboendarterectomy (PEA) is the main method of treatment for patients with chronic thromboembolic pulmonary hypertension (CTEPH). The residual pulmonary hypertension (PH) after CTEPH surgical treatment is a risk factor with increasing of hospital mortality. Objective: To analyze and evaluate the results of PEA in patients with different persistent time of medical history as a possible prognostic factor of residual PH and outcome. Methods: Retrospective and prospective analysis of the PEA results in 87 patients operated on from April 2012 to February 2022 was conducted. The patients were divided into 3 groups. The 1st group - 45 patients with a medical history from 3 months to 1 year, the 2nd - 20 patients from 1 year to 3 years and the 3rd - 22 patients with long-term history more than 3 years. Results: The average age of the patients was 48.7 ± 13.5 years, including 56.7 % males and 43.3 % females. Due to New York Heart Association (NYHA), 7 (8.0%) patients preoperatively belonged to class II, 60 (69.0%) to class III and 20 (23.0%) to class IV. Postoperatively the mean pulmonary artery pressure (mPAP mmHg) and  pulmonary vascular resistance (PVR dyn·s·cm⁻⁵) significantly decreased in all groups (mPAP :1st group from 45±13 to 23±6, 2 nd – from 49±14 to 25±6 and 3 rd – from 58±12 to 31±7; PVR: 1st group from 797±262 to 290±135, 2 nd – from 925±383 to 376±159 and 3 rd – from 1248±332 to 505±189). Hospital mortality after PEA was 0 in patients with medical history less than 1 year, 5% from 1 to 3 years and 31% in patients with long- term anamnesis. Conclusions: PEA is an effective surgery with mPAP and PVR decreasing in the early postoperative period. However, long-term medical history and PVR >1000 dyn·s·cm⁻⁵ are very important risk factors with increasing of hospital mortality.