The purpose of the study is to determine the diurnal variation of rectal diameter in healthy and constipated children using transabdominal ultrasound.

Constipated Inclusion Criteria:

• Children from 4 to 12 years with previously diagnosed simple constipation defined by ROME III criteria, which at inclusion is in maintenance therapy with PEG + E and has been in treatment for at least 1 month.

Exclusion Criteria:

• Children with known organic causes of constipation, including Hirschsprungs disease, spinal and anal congenital abnormalities, previous surgery on the colon, inflammatory bowel disease, allergy and metabolic or endocrine diseases.
• Children receiving drugs known to affect bowel function during a 2 month period before initiation besides laxatives.

Healthy inclusion Criteria:

• Children between 4 and 12 years of age.

Healthy exclusion Criteria:

• Children with known organic causes of constipation, including Hirschsprungs disease, spinal and anal congenital abnormalities, previous surgery on the colon, inflammatory bowel disease, allergy and metabolic or endocrine diseases.
• Children receiving drugs known to affect bowel function during a 2 month period before initiation.
• Children with a previous history of constipation, fecal incontinence and / or urinary tract infections.

Constipated children are recruited from the outpatient clinic at Kolding pediatric department. A list of patients which have been given the diagnose constipation are drawn from the computer and reviewed. Children between 4-12 years who fulfill the Rome III criteria of constipation and have been taking PEG maintenance treatment at least 1 month, are contacted by telephone for possible participation in the study.

Healthy participants without constipation or other diseases affecting the gastrointestinal tract were recruited among the employees of the Department of Pediatrics at Kolding Hospital.

Written informed consent was obtained from both parents before any procedures were initiated.