Summary: In all age groups, functional constipation is the most common functional gastrointestinal disorder. The use of polyethylene glycol (PEG), an osmotic laxative, orally with or without electrolytes is recommended as the first-line treatment for children presenting with fecal impaction and as the first-line maintenance treatment. The first part of the article summarizes current data on functional constipation in children. In the second part, the focus is on PEG, its mechanism of action, efficacy, and safety.