A total of 100 renal cell carcinomas were prospectively examined for renal sinus invasion, 74 clear cell renal cell carcinomas (CC), 3 renal cell carcinomas, unclassified (RUC), 16 papillary renal cell carcinomas (PapC), and 7 chromophobe renal cell carcinomas (ChC). Using the 2002 TNM staging formulation, 49 tumors were T1, 5 were T2, and 46 were T3 or T4. Renal sinus invasion occurred more often than renal capsule invasion. No tumor invaded the capsule that did not also invade the sinus. Renal sinus invasion correlated with Fuhrman grade; 17% of grades 1/2 tumors invaded the sinus, while 71% of grade 3/4 tumor invaded the sinus (P < 0.001). Sinus invasion correlated with tumor type; 2 of 23 PapC and ChC invaded the sinus compared with 44 of 77 CC and RUC. Sinus invasion occurred in approximately 16% of tumors 1 to 4 cm in size, then abruptly increased for larger tumors (P < 0.001). When tumors are staged by the 1997 and 2002 TNM formulation, renal sinus invasion upstaged 28% of cases stage T1 or T2 by the 1997 formulation, to T3 using the 2002 criteria. In conclusion, renal sinus invasion is the most common site of extrarenal extension of renal carcinoma and correlates with tumor type, grade and size. Appropriate evaluation for sinus invasion reduces the incidence of T1b and T2 CC tumors, limiting prognostic utility and suggesting reassessment of the T1 and T2 stage designations.