Constipation is a common problem in children. It occurs in up to 10%, although only 3% of parents actually seek advice from a health care practitioner. Constipation is generally described as the infrequent passage of stools (bowel movements) or the passage of hard stools. Any definition of constipation depends on how often the child normally passes stools and the normal consistency of his or her stools.

Most children with constipation have no underlying medical condition. They often are labelled as having functional constipation or acquired megacolon. In most cases, childhood constipation develops when the child begins to associate pain with defaecation. Once pain is associated with bowel movements, the child begins to withhold stools in an attempt to avoid discomfort. As stool withholding continues, the rectum gradually accommodates, and the normal urge to defaecate gradually disappears. The infrequent passage of very large and hard stools reinforces the child's association of pain with defaecation, resulting in worsening stool retention and progressively more abnormal defaecation dynamics with anal sphincter spasm. Chronic rectal distension ultimately results in both loss of rectal sensitivity, and loss of urge to defaecate, which can lead to faecal incontinence (i.e., encopresis).