Mucinous tubular and spindle cell carcinoma of the kidney (MTSCC-K) is an extremely rare carcinoma of the kidney, which develops by malignant differentiation of the collecting ducts or the loop of Henle. The tumor can occur at all ages, with 4 times higher prevalence in females than in males. A 62-year-old female patient presented with an asymptomatic mass lesion in the left kidney. The ultrasound revealed a hyperechogenic mass lesion measuring 4 cm in diameter and centrally located in the left kidney. Computed tomography (CT) revealed an isodense mass lesion measuring 4 cm in diameter and posterolaterally located in the left kidney. Magnetic resonance imaging revealed a renal mass of 4 cm in diameter with hypervascular contrast uptake. For primary staging, (18)F-fluorodeoxyglucose-positron-emission tomography ((18)FDG-PET)/CT revealed left renal cell carcinoma (RCC) with a maximum standard uptake value of 6.7. The patient underwent transperitoneal radical nephrectomy. The immunohistochemical examination revealed MTSCC-K. (18)FDG-PET/CT provides 81-89% sensitivity and 83-100% specificity in primary staging of the renal cancers, in diagnosing metastatic RCC, and monitoring the response to therapy. Its use in the staging of MTSCC of the kidney has not been previously described in the literature. This case highlights the usefulness of (18)FDG-PET/CT in the staging of this rare tumor.