Background: Activating DNA sequence genomic alterations (GA) in the FGFR3 gene are known oncodrivers and relevant precision targets for patients with urothelial carcinoma. THOR-1 trial showed a significant overall survival benefit with erdafitinib (FGFR inhibitor) vs chemotherapy (taxane or vinflunine) in patients with advanced urothelial carcinoma of the bladder (UCB) or upper tract urothelial carcinoma (UTUC). PROOF-302 trial showed higher frequency of FGFR3 GA in UTUC (30%) vs UCB (13%). We sought to explore differences in frequency of FGFR3 alterations and the genomic landscapes of FGFR3-altered UCB, ureteral urothelial carcinoma (UUC) and renal pelvic urothelial carcinoma (RPUC). Methods: 10,798 UCB and 2,392 UTUC (871 UUC and 1521 RPUC) underwent hybrid capture-based comprehensive genomic profiling (CGP) to assess all classes of GA and measure MSI status, TMB level, genomic ancestry, genomic signature, germline mutations and HRD score. PD-L1 was determined by IHC Dako 22C3 using the TPS system. Results were compared using the Fisher Exact method with the Benjamini-Hochberg adjustment. Results:FGFR3mut+ status was significantly higher in RPUC (27.8%), followed by UUC (22.0%), and UCB (18.1%) (P<.0001) (Table). Patients with UCB were more often male compared to patients with UTUC. Median age, EUR ancestry, and GA/tumor were similar. “Targetable” GA in ERBB2 (P=.03), PIK3CA(P=.05), KDM6A (P=.0009)were more frequent in FGFR3mut+ UCB vs FGFR3mut+ UTUC. Targetable GA in PTEN, TSC1 and MTAP currently associated with drugs tested in trials were similar in UBC and UTUC. The KEGG ERBB and VEGF signaling pathways were more frequently identified in UCB (P=.036) and the MMR pathway more frequently identified in UTUC (P=.014). The HRD signature was similar in the groups. MSI-high status was significantly higher in UTUC vs UCB, but there was no significant difference in TMB or PD-L1 expression levels. Conclusions: Although histologically similar, the genomic landscape of FGFR3mut+ RPUC and UUC has notable differences with FGFR3mut+ UCB. Limitations include lack of clinical data annotation, inherent selection biases, and the retrospective nature of this work. Findings may impact clinical trial designs for UCB and UTUC, including evaluating combinations of anti-FGFR3 with other agents. CGP may also inform resistance mechanisms and putative biomarkers of response.