Context: Functional constipation (FC) and IRRITABLE BOWEL SYNDROME (IBS) represent very common pediatric functional gastrointestinal disorders (FGIDs). Controversial results have suggested a potential role of food allergy as a trigger of functional BOWEL symptoms.Evidence Acquisition: This review summarizes the literature regarding the role of allergic diseases in children with FC and IBS and discusses the hypothesis of the pathogenesis of constipation due to cow’s milk protein allergy (CMPA).We searched systematic reviews, guidelines, or original data in PubMed, MEDLINE, and the Cochrane central register of controlled trials.Results: The pathogenesis of FGIDs remains elusive and is likely multifactorial. Among these factors, adverse reactions to food may play a pathogenic role. Some features, such as abnormal BOWEL motility, visceral hypersensitivity, and changes in mucus composition caused by inflammation of the gastrointestinal wall, have been found both in IBS or FC and in food allergy. Since 1978, an increasing number of reports have suggested a relationship between CMPA and FC. Two randomized controlled studies conducted in children showed that CMPA may induce chronic FC; one study indicated that fermentable oligosaccharide, disaccharide, and monosaccharide polyols (FODMAP) foods may play a role in triggering IBS.Conclusions: Food allergy in children with chronic constipation should be identified using an oral food challenge after being on a diet free of cow’s milk. A diet low in FODMAPs might also be recommended for children with IBS. This approach could be suggested for children with chronic FC and IBS, especially when they do not respond to standard treatment. However, it should also be considered that a minority of patients with FC or IBS could respond to an elimination diet. Further studies are needed to understand the complex pathogenic mechanisms of FGIDs; they also might be helpful to recognize markers for identifying children with IBS and FC caused by foods and to improve their management.