Mediastinal tumors represent a wide diversity of nosological entities and occur at any age. There are congenital and acquired neoplasms that can not only arise from mediastinal tissues, but can also involve them during lung pathological processes or distant metastases in malignant tumors at various sites. The most sparing, minimally invasive technique for morphological verification is ultrasound-guided transthoracic core-needle biopsy; however, the diagnostic value, sensitivity, and specificity of the technique vary widely in different forms of mediastinal tumors and according to the experience of a facility. Material and methods. In 2007 to 2017, the Department of Thoracic Surgery, P.A. Herzen Moscow Oncology Research Institute, performed 89 transthoracic core-needle biopsies in 80 patients (47 women, 33 men) with primary tumor and mediastinal metastasis. Forty-seven standard biopsies and 43 multifocal ones (33 from two points and 10 from three ones) were carried out. Results. The final histological diagnosis was established by ultrasound-guided transthoracic mediastinal biopsy in 67 (84%) cases of the total number of patients. Fifty-seven (85%) patients were diagnosed with malignant tumor; its process was benign in 10 (15%) cases. The presented biopsy material was uninformative in 19 (23.6%) of 21 patients. The amount of the material fell short of adequate tumor immunophenotyping in 16 cases. Rebiopsy was carried out in 7 patients, which permitted a final diagnosis to be made in 6 cases. Due to the inefficiency of transthoracic biopsy, 13 patients underwent diagnostic parasternal mediastinotomy, open tumor biopsy. A final diagnosis was established in all the patients. Conclusion. Ultrasound-guided transthoracic mediastinal biopsy is a safe and reliable technique for morphological verification, which is characterized by a high diagnostic accuracy. The overall procedure effectiveness is 82.7%. In the presence of a tumor necrosis area, multifocal biopsy increases the informative value of biopsy material. In the group of patients with suspected lymphoproliferative disease complicated by the course of the tumor process, open tumor biopsy is indicated if the first attempt of transthoracic biopsy fails to provide information.