BACKGROUND: C-reactive protein (CRP) is commonly used to assess systemic inflammation, yet its prognostic value in acute myocarditis remains uncertain. Evidence is limited by heterogeneous populations, variable CRP thresholds and differing outcome definitions. We therefore aimed to evaluate whether CRP levels measured at presentation are associated with 90-day clinical outcomes in adults hospitalised with acute myocarditis. METHODS: Using the TriNetX Research Network, we identified 3615 adults hospitalised with acute myocarditis between 2005 and 2025. Patients were stratified according to baseline CRP <10 mg/L (n=1001) vs ≥10 mg/L (n=2614). Propensity score matching (1:1) was performed using age, sex and race. The primary outcome was a 90-day composite of all-cause death and tachyarrhythmias (atrial fibrillation, ventricular tachycardia, ventricular fibrillation or torsades de pointes). Secondary outcomes included the individual components. RESULTS: In the unmatched cohort, patients with CRP <10 mg/L had a numerically higher 90-day incidence of the primary composite outcome compared with those with CRP ≥10 mg/L (16.4% vs 14.0%; log-rank p=0.087; HR 1.17, 95% CI 0.98 to 1.41), driven by a borderline higher incidence of tachyarrhythmias (14.1% vs 11.7%; log-rank p=0.059; HR 1.21, 95% CI 0.99 to 1.48), while all-cause mortality was similar between groups. After propensity score matching, the 90-day incidence of the primary composite outcome was virtually identical in the CRP <10 mg/L and CRP ≥10 mg/L groups (16.4% vs 16.9%; log-rank p=0.735; HR 0.96, 95% CI 0.78 to 1.19). Individual endpoints (tachyarrhythmias and all-cause mortality) were also similar, with no statistically significant differences. CONCLUSION: In this large dataset analysis, elevated baseline CRP was frequent in patients with acute myocarditis and was not consistently associated with 90-day adverse outcomes. A single CRP measurement at presentation appears to have limited value for risk stratification in this setting.