Background: Indicators of body composition and nutritional status, such as lumbar skeletal muscle index (SMI, cm²/m²) and hypoalbuminemia, are associated with adverse outcomes following surgery for localized renal cell carcinoma (RCC) but have yet to be described in patients with RCC and venous tumor thrombus. We hypothesize that preoperative sarcopenia, a severe deficit in lean muscle mass, and hypoalbuminemia will be associated with decreased overall survival (OS) and cancer specific survival (CSS) in nonmetastatic RCC patients undergoing radical nephrectomy and tumor thrombectomy. Methods: We retrospectively analyzed 103 nonmetastatic RCC patients who underwent radical nephrectomy and tumor thrombectomy from 2005 to 2020. Optimally fit BMI (kg/m²) and sex-stratified sarcopenia thresholds were calculated (BMI<30: SMI<47 for males, SMI<38 for females; BMI≥30: SMI<54 for males, SMI<47 for females). Sarcopenia and albumin risk groups were created based on their individual hazard ratios on univariable analysis and defined as low-risk (non-sarcopenic, normal albumin), medium-risk (non-sarcopenic, hypoalbuminemia), high-risk (sarcopenic, normal albumin), and very high-risk (sarcopenic, hypoalbuminemia). Associations between independent and combined sarcopenia and hypoalbuminemia (albumin<3.5 g/dL) with OS and CSS were evaluated using multivariable and Kaplan-Meier analyses. Results: Prevalence of sarcopenia and hypoalbuminemia were 51.2% and 44.7%, respectively. Median follow up time was 24.8 months and median time from preoperative imaging to surgery was 21 days. Sarcopenia was an independent predictor of OS (p=0.003) and CSS (p=0.006) whereas hypoalbuminemia was not (OS: p=0.096; CSS: p=0.718). When analyzing sarcopenia and albumin in combination, the high and very high-risk groups were significantly associated with decreased OS (high-risk: p=0.011; very high-risk: p<0.001) and CSS (high-risk: p=0.011; very high-risk: p=0.017). Kaplan-Meier curves showed a stepwise decline in median OS (p=0.0071) and CSS (p=0.0068) times with increasing risk. Conclusions: Simultaneous sarcopenia and hypoalbuminemia were associated with nearly a seven-fold decrease in OS and CSS in patients undergoing surgery for nonmetastatic RCC with IVC tumor thrombus.