Purpose: The purpose of this review was to critically analyse the current evidence investigating the effect of an athlete's hydration status on physical performance. Methods: A literature search of multiple databases was used to identify studies that met the inclusion criteria for this review. The included studies were then critically appraised using the Downs and Black protocol. Results: Nine articles were found to meet the inclusion criteria, with an average score of 79% for methodological quality representative of a "high" standard of research. Conclusion: The evidence suggests that dehydration has a negative impact on physical performance for activities lasting more than 30 s in duration. However dehydration was found to have no significant impact on physical performance for activities lasting less than 15 s in duration.