Introduction: Dehydration is an important complication for sick children. The Clinical Dehydration Scale for Children (CDSC) measures dehydration based on four clinical signs.Objective: Evaluate the correlation between the CDSC categories and markers of dehydration in children aged 1 month to 5 years visiting an emergency department (ED) for vomiting and/or diarrhea.Method : An international prospective cohort study performed in three pediatric ED in 2009. Participants were a convenience sample of children aged 1 to 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 CDSC. A few days after recovery, another research assistant weighted 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 admission, intra-venous use and inter-rater agreement. Sample size was estimated to have at least 10 participants in each CDSC categories.Results : During the study period, 251 children were recruited and information regarding weight and dehydration scores was complete for 206 (82%). According to the CDSC, 59 had no dehydration, 132 some dehydration and 14 moderate/severe dehydration. On logistic regression, the CDSC categories were predictors of severe dehydration, intra-venous re-hydration and hospitalization (p < 0.01 for all). Good inter-rater correlation was measured among participants (linear weighted Kappa score of 0.65 (95%CI 0.43-0.87)).Conclusion : CDSC categories correlate with markers of dehydration for young children complaining of vomiting and/or diarrhea in the ED.