PURPOSE: Tumor necrosis is associated with a poor oncological outcome in patients with upper tract urothelial carcinoma and other malignancies. We validated the association of tumor necrosis with pathological features and clinical outcomes in a large international cohort of patients with upper tract urothelial carcinoma treated with radical nephroureterectomy. MATERIAL AND METHODS: This retrospective study included 754 patients treated with radical nephroureterectomy at a total of 9 centers. Tumor necrosis was scored as greater than 10% of tumor area based on microscopic evaluation. RESULTS: Tumor necrosis was present in 165 specimens (21.9%). The prevalence of tumor necrosis increased with advancing pathological stage, including 7%, 10.6% and 50% for T1, T2 and T3-4, respectively (p