Background. Wilm’s tumor, or nephroblastoma, is one of the most common solid malignant neoplasms in children, occurring almost exclusively in the kidneys. Extrarenal Wilm’s tumors are extremely rare, and their clinical presentation depends on the location of the tumor. The diagnosis of extrarenal Wilm’s tumor is almost always made after resection and histological evaluation of the tumor.
Description of the clinical case. The article presents the case of a 10-year-old boy with an extrarenal Wilm’s tumor located in the retroperitoneal space. He applied to the local outpatient clinic with complaints of abdominal pain, an increase in the abdomen in volume. According to the ultrasound examination of the abdominal organs, the formation of the retroperitoneal space was revealed. In Tashkent City Branch of the Republican Specialized Scientific and Practical Medical Center of Oncology and Radiology, magnetic resonance imaging of the abdominal organs with intravenous contrast was performed. In the projection of the right kidney, a round formation with the size of 11×11×15 cm was revealed. The patient underwent a high-tech operation from the point of view of oncosurgery and reconstructive surgery. In the postoperative period, the tumor was classified as intermediate risk stage III (invasion of the tumor beyond the capsule with a positive para-aortic lymph node). Adjuvant chemotherapy was performed after surgical treatment. The total duration of treatment was 5 months. The patient is under observation. The duration of remission is 8 months.
Conclusion. It is appropriate to assume the extrarenal Wilm’s tumor when evaluating patients with asymptomatic abdominal distension, since an untimely diagnosis may delay appropriate therapy.

Keywords: Wilm’s tumor, retroperitoneal tumor, adjuvant chemotherapy, surgical treatment