Aim: This article examines the evidence for a role of cow's milk protein in chronic functional constipation in children. Methods: A literature search was conducted using Ovid and Pubmed, the Cochrane data bases, CINHAHL and EBSCO. Keywords searched included: constipation, cow's milk, intolerance, allergy, children and intestinal motility. This systematic review focused on dietary intervention studies in children (aged from 7 days to 15 years) with chronic functional constipation. All articles were required to include measures of cow's milk protein allergy or intolerance and include resolution of constipation as an outcome measure. Results: The keyword search identified 125 articles. Seven of these articles met the criteria for inclusion, including one double-blind, randomised controlled trial. The results of this review provide support for the hypothesis that a proportion of children with chronic functional constipation respond well to the removal of cow's milk protein from the diet, particularly if serum analysis shows abnormalities of immune mechanisms. Conclusion: The evidence surrounding cow's milk constipation was limited with only one of the assessed studies being at level II of evidence according to the NHMRC. In order to develop evidence-based guidelines, further high-level evidence is required to clarify the physiological, immunological and biochemical changes that occur in some constipated children who respond to the removal of cow's milk protein from the diet.