This report discusses the new cytogenetic classification of renal cell carcinoma (RCC) and its biological and clinical significance. It describes the four major types (clear cell, chromophil, chromophobe, and collecting duct) as well as rarer entities, such as small cell carcinoma, cystic RCC, rhabdoid variant of RCC, and unclassified RCC. Sarcomatoid carcinomas are a diverse group representing high-grade transformation of the other types. In addition to a description of the pathologic findings, there is a discussion of tumor markers and prognostic indicators. The clinical significance of the classification is discussed, with reference to recent reports.