Congenital mesoblastic nephroma (CMN) is a rare renal tumor of young children with intermediate biological behavior, accounting for 3.5-4% of all renal tumors in children. СMN is characterized by a favorable prognosis in case of radical surgical treatment. Relapses of CMN are considered to be quite a rare occurrence (4% of all cases), however, both local and metastatic relapses are possible. There are no fully standardized treatment approaches for patients with relapsed CMN. In our study, we performed a retrospective analysis of patients (n = 3) with a verified relapse of CMN who had received treatment at the D. Rogachev NMRCPHOI between 2012 to 2022 (132 months). At relapse, all the patients underwent at least one part of treatment at the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation. The diagnosis of CMN was established at the Pathology Department of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation, based on a histological examination. The patients with the cellular histological subtype of CMN underwent fluorescent in situ hybridization testing for ETV6 gene rearrangements. The demographic characteristics, clinical data, the extent of initial treatment and relapse therapy were assessed. Here, we describe three clinical cases of relapse in patients with CMN. The median age at initial diagnosis was 0.8 months (range 0.7–1.4). Our analysis of the extent of primary surgical treatment, including nephrectomy, in all cases revealed the following factors associated with a higher risk of relapse: preoperative tumor rupture – 1, intraoperative tumor rupture – 1, inability to confirm tumor-free margins – 1. The distribution of histological subtypes was as following: classical CMN (n = 1), cellular CMN (n = 1), and mixed CMN (n = 1). One patient had local stage II and 2 patients had local stage III. The median time from diagnosis to disease relapse was 0.8 months (range 2.3–4.3). One patient with mixed CMN died 10.6 months after diagnosis from complications of intensive therapy carried out for extremely aggressive relapse. Two patients are alive after repeated surgical treatment (R1 resection) and adjuvant therapy with actinomycin D and vincristine (AV regimen) for 27 weeks in one case, and neoadjuvant therapy (AV regimen for 4 weeks), delayed surgery (R0 resection), and adjuvant therapy (AV regimen for 4 weeks) in the other case. These patients were followed up for 92.2 and 21.3 months, respectively. By acknowledging the possibility of recurrent CMN, it seems important to provide multidisciplinary clinical care to young children with renal tumors involving a detailed planning of surgical procedures, radical surgeries in accordance with practice guidelines and standards in surgical oncology, and careful follow-up, especially during the first year after surgery. The patients' parents gave consent to the use of their children's data, including photographs, for research purposes and in publications.