OBJECTIVE: The purpose of this article is to determine whether the relationship between a renal cell carcinoma and the renal sinus fat on contrast-enhanced CT could predict muscular venous branch invasion and the type of surgery needed. MATERIALS AND METHODS: A total of 115 consecutive patients underwent pre-operative contrast-enhanced CT between August 2011 and December 2011. Without access to histopathologic information, on nephrographic phase contrast-enhanced CT images, two radiologists independently determined whether the renal tumor was in contact with the renal sinus fat or separated from the renal sinus fat. Interreader agreements and performance characteristics of imaging tests were calculated, and histopathologic analysis served as the standard of reference. RESULTS: Histopathologic analysis identified 115 renal tumors, 90% (103/115) of which were renal cell carcinomas. Thirty-nine percent (31/80) of renal cell carcinomas that abutted the renal sinus fat on CT displayed muscular venous branch invasion on histopathologic analysis. Patients with renal cell carcinomas separated from the renal sinus fat were more likely to undergo partial nephrectomies (96% [22/23]; p = 0.013). Sensitivity and specificity for the identification of muscular venous branch invasion on CT were 94% (95% CI, 80-99%) and 30% (20-42%), respectively. Interreader agreement of visual assessment was excellent (κ = 0.87; 95% CI, 0.81-0.92). CONCLUSION: If a renal cell carcinoma was separated from the renal sinus fat on CT, the likelihood of muscular venous branch invasion being identified by histopathologic analysis was significantly decreased, and the patient was more likely to undergo a partial nephrectomy.