Renal cell carcinoma unclassified is defined as renal cell carcinoma that cannot be pathologically categorized as any of the known pathologic types. Renal cell carcinoma unclassified includes, but is not limited to, the following types: renal cell carcinoma containing more than one pathological feature of renal cell carcinoma, renal cell carcinoma with mucus secretion, renal cell carcinoma with unclassified epithelial components, low-grade or high-grade unclassified eosinophilic tumors, and tumors with sarcomatous morphology and lack of identifiable epithelial components. Renal cell carcinoma unclassified usually accounts for less than 5% of renal tumors, is morphologically variable, the tumors are often large and extensively infiltrate the kidney, and the prognosis usually depends on the stage and nuclear grade of the tumor. If diagnosed with renal cell carcinoma unclassified, patients need to consult the doctor for timely examination and early treatment.