Introduction: Upper urinary tract urothelial carcinoma is rare and accounts for about 5-10% of urothelial carcinomas. Grossly it may arise anywhere between the renal calyces to the distal ureter. Case Report: We report a very rare case of a 65-year-old male whose clinical and radiological diagnosis was pyelonephritis and non-functioning kidney but it turned out to be an unusual presentation of the tumour involving the entire kidney mimicking renal cell carcinoma. The final diagnosis of a high grade invasive urothelial carcinoma with squamous differentiation was rendered on histopathology highlighting the very rare presentation. Conclusion: We report a rare case of high-grade urothelial carcinoma in a non-functioning kidney.