Background <p>Renal tumor and inferior vena cava tumor thrombus (RT-IVCTT), as a unique model for investigating congestive renal injury, remains largely unexplored. Although chronic kidney disease significantly correlates with postoperative adverse events and long-term prognosis in both renal tumor and pan-cancer settings, there is no large-scale evidence specifically addressing RT-IVCTT. This study aimed to identify risk factors of preoperative renal dysfunction (pre-RD) and evaluate its contribution as a predictor for prognosis in patients with RT-IVCTT.</p> Patients and Methods <p>Consecutive postoperative patients with RT-IVCTT and no evidence of distant metastasis (<i>n</i> = 208) were retrospectively enrolled between June 2013 and June 2023. Preoperative estimated glomerular filtration rate (pre-eGFR) (mL/min/1.73 m²) was classified into four categories: ≥ 120, 90–120, 60–90, and &lt; 60, and clinical data were analyzed to determine a meaningful cutoff. Multivariate logistic and Cox regression models were employed to identify risk factors of pre-RD and prognosis in patients with RT-IVCTT, respectively.</p> Results <p>Pre-RD, defined as pre-eGFR &lt; 90 mL/min/1.73 m², was found in 59 patients (28.4%). Pre-RD was associated with increased operative time, intraoperative blood transfusion, extended intensive care unit stay, major complications and long-term survival. Age &gt; 56 years, body mass index &gt; 24 kg/m², left-sided tumors, and IVC obstruction &gt; 75% were independent risk factors for pre-RD. Survival analysis revealed that pre-RD was an independent risk factor for poorer overall survival.</p> Conclusions <p>Pre-RD is an independent risk factor for diminished long-term survival after surgery. Hemodynamic changes from IVC obstruction are associated with pre-RD. eGFR-based renal function assessments may improve perioperative management.</p> <p>Chinese Clinical Trial Registry: ChiCTR2400089649.</p>