An increasing incidence of food allergy, especially to cow's milk proteins, is observed in children living in the industrialized regions of the world. In some cases responding to an eviction diet excluding offending foods, the 'functional' constipation can be caused by inflammation of the intestinal wall infiltrated by eosinophils. Understanding the complex mechanisms involved could help to improve the management of idiopathic functional constipation in children by addressing the aetiology instead of treating the symptoms.