Gemcitabine (GEM) is currently a standard chemotherapeutic agent for metastatic urothelial carcinoma (mUC). Fever isknown to be an adverse effect of GEM ; however, itsincidence, etiology and clinical significance have not been evaluated. The objective of this study was to elucidate the characteristics and clinical significance of fever associated with GEM in patients with mUC receiving GEM plus cisplatin (GC) chemotherapy. Between 2005 and 2014, 184 patientswith mUC who received first-line GC therapy at 10 institutions were enrolled. GEM-associated fever (GEMAF) was defined as a body temperature ≥37.5ºC within 96 hours after administration of GEM with no evidence of specific conditions causing fever including infection. Clinical parametersbefore GC therapy were evaluated to determine predictorsof GEMAF. Furthermore, the impact of GEMAF on clinical outcomeswasals o evaluated. The median age was70 years and median follow-up was14.2 months. GEMAF wasobs erved in 44 patients (23.9%). In multivariate analysis, elevated C-reactive protein (CRP) before chemotherapy was an independent predictive factor for GEMAF (oddsratio 2.450, p＝0.041). There was a significant difference in progression-free survival (median 6.7 vs 8.0 months, p＝0.031) and cancer-specific survival (median 12.0 vs 15.8 months, p＝0.045) between patients with and without GEMAF. Results of this study suggest that GEMAF is a common adverse event of GC therapy for mUC and can be a poor prognostic factor. GEMAF may be associated with systemic inflammatory response induced by the tumor in patients with mUC.