Background: CRP is an acute phase reactant synthesized by hepatocytes in response to inflammatory cytokines including interleukin-6. Peripheral blood CRP, a routinely measured analyte, may reflect tumor microenvironments skewed towards tumor-promoting inflammation. CRP may therefore represent an attractive biomarker to select patients with bladder cancer (BCa) more likely to benefit from therapies directed at modulating tumor-promoting inflammation. Methods: A systematic review was performed to identify studies reporting outcomes based on pre-treatment CRP values in patients with localized and advanced BCa and urothelial carcinoma (UC). The hazard ratio (HR) of overall survival (OS), cancer-specific survival (CSS), relapse-free survival (RFS), and progression-free survival (PFS) between groups with high and low CRP values as defined in each study was extracted. Meta-analysis using the random-effect model was performed to pool HR. Meta-regression analysis was conducted to assess the relationship between CRP cutoff and HR for OS. Subgroup analyses were performed according to clinical disease state and therapies administered. Heterogeneity was assessed using I² statistics. Results: Overall, 938 articles were identified at initial screening; 22 studies comprising 2,899 patients were included in the meta-analysis. For OS, 17 datasets from 16 studies were used. High CRP levels were associated with decreased OS (HR=2.03, 95%CI:1.67-2.47, p<0.01) although high heterogeneity was observed (I²=91%). Subgroup analyses according to anticancer interventions showed that high CRP values were related to shorter OS, particularly in patients treated with immune checkpoint blockade (ICB; HR=1.78, 95%CI: 1.47-2.15, p<0.01). In meta-regression analysis, the correlation between CRP cutoff value and OS HR was not observed when all 16 studies were considered (Regression coefficient=0.03, 95%CI: -0.13-0.18, p=0.73). However, CRP cutoff value was significantly associated with the HR for OS (Regression coefficient=-0.21, 95%CI: -0.36 to -0.06, p=0.01) when the analysis was limited to eight studies assessing ICB in advanced BCa/UC. Pooled HR of CSS, RFS, and PFS is shown in Table. Conclusions: High CRP values were associated with poorer clinical outcomes in patients with BCa/UC, particularly among patients with advanced disease treated with ICB. CRP may represent an attractive biomarker to enrich populations more likely to benefit from therapies that modulate tumor-promoting inflammation.