The prognostic impact of multifocal upper-tract urothelial carcinoma (UTUC) is poorly understood. To investigate the association between tumor multifocality and clinicopathologic features and outcomes of UTUC in patients managed by radical nephroureterectomy (RNU). The study included 2492 patients treated with either open or laparoscopic RNU. Tumor and patient characteristics included tumor stage, tumor grade, lymph node status, lymphovascular invasion (LVI), tumor architecture, tumor location, unifocal or multifocal disease, gender, age, history of bladder cancer (BCa), Eastern Cooperative Oncology Group (ECOG) performance status (PS), and adjuvant chemotherapy. tumor multifocality of UTUC was defined as the synchronous presence of multiple tumors in the renal pelvis or ureter. All patients were treated with either open or laparoscopic RNU. Univariable and multivariable models tested the effect of tumor multifocality on disease progression and cancer-specific mortality. Five hundred ninety patients (23.7%) had tumor multifocality at the time of RNU. The median follow-up was 45 mo (interquartile range [IQR]: 0-101). Tumor multifocality was significantly associated with a history of previous BCa (p=0.032), lymph node involvement (p=0.036), tumor location in the ureter (p=0.003), higher tumor stage (p<0.001), higher tumor grade (p<0.001), sessile tumor architecture (p=0.003), and LVI (p=0.001). In organ-confined patients, tumor multifocality was an independent predictor of both disease progression (hazard ratio [HR]: 1.43; p=0.019) and cancer-specific mortality (HR: 1.46; p=0.027). When assessed in all patients, tumor multifocality was associated with both disease progression and cancer-specific mortality in univariable (p=0.005 and p=0.006, respectively) but not in multivariable analyses (p=0.468 and p=0.798, respectively). The main limitation is the retrospective design of the study. Tumor multifocality is an independent prognosticator of disease progression and cancer-specific mortality in patients with organ-confined UTUC treated with RNU. Multifocal organ-confined patients with UTUC may need closer follow-up. Integration of tumor multifocality with other factors may help identify those patients who would benefit from multimodal therapy. Copyright © 2011 European Association of Urology. Published by Elsevier B.V. All rights reserved.