Abstract: Background: leiomyosarcoma of veins is a rare group of sarcomas of mesenchymal origin, which develops from smooth muscle cells of vascular . Vascular leiomyosarcoma occurs in 2-5% and have a slow growth. It is rather difficult to diagnose this disease on the basis of only clinical symptoms, most often patients are worried about oedema and pain in lower limbs. To establish the diagnosis, it is necessary to use data of instrumental methods of examination, such as ultrasound, magnetic resonance imaging (MRI) and multispiral computed tomography (MSCT) with intravenous contrast enhancement, which allow to determine the tumor localization, prevalence, involvement of the vessel wall in the process, as well as to exclude distant metastases. The final diagnosis is made according to immunohistochemical studies. Aim: was to study the importance of radiadiagnostics methods in case of such rare disease as leiomyosarcoma of the external iliac vein. Material and methods: 67-year-old woman with complaints of oedema of the lower limb, was examined: an ultrasound study of inferior vena cava and veins of lower limbs, magnetic resonance imaging (MRI) and multispiral computed tomography (MSCT) with contrast enhancement, fine-needle aspiration biopsy Patient underwent operation: «removal of the pelvic retroperitoneal tumor with resection of the external iliac vein' segment and pelvic lymph node dissection.» Histological examination: leiomyosarcoma, G2 FNCLCC. Results: control MSCT - data on the recurrence of the iliac vein tumor and metastatic lesion of organs of chest, abdominal and pelvic cavity were not obtained. Conclusions: a complex of diagnostic methods allows you to properly diagnose. And among these methods, multiphase computed tomography is one of the best imaging method, which shows not only the localization of the tumor, but also helps in staging, excluding or confirming vein thrombosis, solving the issue of resectability of the tumor and identifying distant metastasis. References 1. Le Minh T, Cazaban D, Michaud J. et al. Great saphenous vein leiomyosarcoma: a rare malignant tumor of the extremity-two case reports. Ann Vasc Surg. 2004; 18(2): 234-236. 2. Yucel Yankol, Nesimi Mecit, Turan Kanmaz et al. Leiomyosarcoma of the retrohepatic vena cava: Report of a case treated with resection and reconstruction with polytetrafluoroethylene vascular graft. Ulus Cerrahi Derg 2015; 31: 162-165. 3. Tripodi E, Zanfagnin V, Fava C. et al. Leiomyosarcoma of the Right Iliac Veins presenting as a pelvic mass: a case report. Obstet. Gynecol. cases Rev. 2015; 2 (3): 1-4. 4. Mei Zhang, MDa, Feng Yan et al. Multimodal ultrasonographic assessment of leiomyosarcoma of the femoral vein in a patient misdiagnosed as having deep vein thrombosis: a case report. Medicine. 2017: 96(46): 1-5. 5. Pavlov A.YU., Garmash S.V., Isaev T.K. i dr. Sovremennye predstavleniya o lejomiosarkomah ven zabryushinnogo prostranstva. Obzor klinicheskih sluchaev. [Modern ideas about leiomyosarcoma veins retroperitoneal space. Review of clinical cases.] Onkourologiya. 2016; 12(2): 92-96 [in Russ]. 6. Watanabe K, Tajino T, Sekiguchi M. et al. h-Caldesmon as a Specific Marker for Smooth Muscle Tumors. Am. J. Clin. Pathol. 2000; 113 (5): 663-668. 7. Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Soft Tissue Tumors. 6th ed. 8. Gonzales-Cantu Ye.M., Tena-Suck M.L., Serna-Reyna S. et al. Leiomyosarcoma of vascular origin: case report. Case Rep. in Clinical Pathology. 2015; 2(4): 60-64 9. Мацко Д.Е. Современные представления о морфологической классификации сарком мягких тканей и их практическое значение. Практическая онкология. 2013; 14 (2): 77-86. 10. Чуканов Е., Никитина О., Марио Таха. Лейомиосаркома нижней полой вены. Променева дагностика, променева терапiя. 2014; 4: 69-72. 11. Ahluwaliya A., Saggar K., Sandhu P. et al. Primary leiomyosarcoma of inferior vena cava: an unusual entity.. Indian Journal of Radiology and Imaging. 2002; 12(4): 515-516. 12. Dzsinich C., Gloviczki P., Van Heerden J. A. et al. Primary venous leiomyosarcoma: a rare but lethal disease. Journal of Vascular Surger. 1992; 15(4): 595-603. 13. Kaprin A.D., Galkin V.N., Zhavoronkov L.P., Ivanov V.K., Ivanov S.A., Romanko Yu.S. Synthesis of basic and applied research is the basis of obtaining high-quality findings and translating them into clinical practice. Radiation and risk. 2017; 26(2): 26-40.