Background: Upper tract urothelial carcinoma (UTUC) poses significant diagnostic challenges due to the limitations of current staging and grading techniques. Ureteroscopic (URS) biopsy is widely used preoperatively, but its accuracy, compared to final pathology, remains variable. Objectives: To evaluate the accuracy and limitations of URS biopsy in the staging and grading of UTUC, using final pathological results from radical nephroureterectomy (RNU) as the reference standard. Methods: This retrospective study included 86 patients who underwent URS biopsy followed by RNU for UTUC at a tertiary institution between 2011 and 2023. Data were collected on patient demographics, tumor characteristics, imaging, and pathology results. The accuracy of URS biopsy in staging and grading was assessed, and its associations with pathological upstaging and non-diagnostic biopsies were statistically analyzed. Results: URS biopsy correctly staged 54.69% of tumors (κ = 0.311 [0.183 – 0.439], p<0.001) and correctly graded 70.93%. (κ = 0.447 [0.303 – 0.592], p<0.001). Pathological upstaging and upgrading occurred in 39.06% and 25.58% of cases, respectively. Non-diagnostic biopsies for both stage and grade were observed in 5.81% of cases, particularly in tumors located in the renal pelvis (p=0.0064). Complementary diagnostic tools, such as computed tomography urography (CTU) and urine cytology, showed limitations, with CTU detecting invasive disease in only 14.29% of cases and urine cytology identifying high-grade tumors in 11.11%. Conclusion: URS biopsy demonstrates limitations in accurately staging and grading UTUC, resulting in a risk of both undertreatment and overtreatment. A multimodal diagnostic approach incorporating imaging, cytology, and clinical judgment is essential to optimizing management decisions and improving oncological outcomes.