Objective: To validate procalcitonin (PCT) level as the best biological marker to distinguish between bacterial and aseptic meningitis in children in the emergency department. Design: Secondary analysis of retrospective multicenter hospital-based cohort studies. Setting: Six pediatric emergency or intensive care units of tertiary care centers in 5 European countries. Participants: Consecutive children aged 29 days to 18 years with acute meningitis. Main Outcome Measures: Univariate analysis and meta-analysis to compare the performance of blood parameters (PCT level, C-reactive protein level, white blood cell count, and neutrophil count) and cerebrospinal fluid parameters (protein level, glucose level, white blood cell count, and neutrophil count) quickly available in the emergency department to distinguish early on between bacterial and aseptic meningitis. Results: Of 198 patients analyzed, 96 had bacterial meningitis. Sensitivity of cerebrospinal fluid Gram staining was 75%. The PCT level had significantly better results than the other markers for area under the receiver operating characteristic curve (0.98; 95% confidence interval, 0.95-0.99; P=.001). At a 0.5-ng/mL threshold, PCT level had 99% sensitivity (95% confidence interval, 97%-100%) and 83% specificity (95% confidence interval, 76%-90%) for distinguishing between bacterial and aseptic meningitis. The diagnostic odds ratio between high PCT level and bacterial meningitis was 139 (95% confidence interval, 39-498), without significant heterogeneity between centers. Conclusions: The PCT level is a strong predictor for distinguishing between bacterial and aseptic meningitis in children in the emergency department. Its combination with other parameters in an effective clinical decision rule could be helpful. ©2008 American Medical Association. All rights reserved.