INTRODUCTION: Dehydration is an important complication for sick children. The Clinical Dehydration Scale for children (CDS) measures dehydration based on 4 clinical signs: general appearance, eyes, saliva, and tears. OBJECTIVE: To validate the association between the CDS and markers of dehydration in children aged 1 month to 5 years visiting emergency departments (EDs) for vomiting and/or diarrhea. METHOD: An international prospective cohort study conducted in 3 university-affiliated EDs in 2009. Participants were a convenience sample of children aged 1-60 months presenting to the ED for acute vomiting and/or diarrhea. Following triage, a research nurse obtained informed consent and evaluated dehydration using the CDS. A few days after recovery, another research assistant weighed participants at home. The primary outcome was the percentage of dehydration calculated by the difference in weight at first evaluation and after recovery. Secondary outcomes included proportion of blood test measurements, intravenous use, hospitalization, and inter-rater agreement. RESULTS: During the study period, 264 children were recruited and data regarding weight and dehydration scores were complete for 219 (83%). According to the CDS, 88 had no dehydration, 159 some dehydration, and 15 moderate or severe dehydration. A Chi-square test showed a statistical association between CDS and weight gain, the occurrence of blood tests, intravenous rehydration, hospitalization, and abnormal plasmatic bicarbonate. Good inter-rater correlation was found among participants (linear weighted Kappa score of 0.65; (95% CI, 0.43-0.87). CONCLUSION: CDS categories correlate with markers of dehydration for young children complaining of vomiting and/or diarrhea in the ED.