The horseshoe kidney (HK) is the most common congenital anomaly of the urinary system, detected in 0.25% of the population. It combines several anatomical defects, including ectopia, malrotation, anomalies of the collecting system, and variations in the blood supply, which are associated with complications that can lead to end-stage renal disease (ESRD). The use of peritoneal dialysis and hemodialysis for this indication is a risk factor for renal cell carcinoma (RCC). HK is associated with various benign and malignant neoplasms. RCC and transitional cell carcinoma are the most common, accounting for 85% and 10% of all cases, respectively. According to the literature, renal transplant recipients are at an increased risk of RCC, predominantly involving their own kidneys. Additionally, kidney recipients who are on persistent immunosuppression are 4–15 times more likely to develop RCC. The article presents a unique case of surgical treatment of HK RCC in a 47-year-old patient who was treated for hypertension from the age of 20, and at the age of 36, he was diagnosed with HK according to ultrasound. At the age of 37, the patient developed ESRD. Peritoneal dialysis and hemodialysis were performed, followed by cadaveric kidney allotransplantation at the age of 42. The patient received continuous immunosuppression. After 5 years, gross hematuria appeared. When examined with native X-ray computed tomography and contrast-enhanced magnetic resonance imaging, a rounded mass with a clear, even outer contour, measuring up to 73×80 mm in size, and a heterogeneous structure without invasion into the fat tissue was visualized in the left half of the HK in the middle segment. Laparoscopic heminephrectomy was performed on the left. Histological examination showed papillary RCC, the resection margins were negative. Creatinine levels were stable. Diagnosis: Stage III renal cell carcinoma pT3aN0M0R0. The patient was assessed after 16 months; no evidence of recurrence was found. The case presented describes a rare case of HK RCC that developed after dialysis and kidney transplantation for ESRD. The patient successfully underwent laparoscopic heminephrectomy with a favorable outcome, with no signs of recurrence of the disease for 16 months. No such cases were reported in the literature. © LLC "KONSILIUM MEDICUM", 2025