Objectives:The aim of the study was to evaluate the effectiveness and safety of 2 different polyethylene glycol (PEG) doses for the maintenance treatment of functional constipation in children.Methods:Children with functional constipation according to the Rome III criteria were randomly assigned to receive PEG 4000 at a dose of either 0.7 g/kg (high-dose group; n=45) or 0.3 g/kg (low-dose group; n=47) for 6 weeks. Adjustment of the therapy was recommended in the event of <3 bowel movements (BM) per week or 3 BM per day. The primary outcome measure was treatment success, defined as 3 BM per week with no fecal soiling during the last week of the intervention.Results:A total of 90 of 92 randomized children, with a mean age of 3.72.1 years, completed the study. In the analysis based on allocated treatment, treatment success was similar in both groups (relative risk 0.9, 95% confidence interval 0.78-1.03). Compared with the high-dose PEG group, the low-dose PEG group had an increased need for therapy adjustment of borderline significance (relative risk 2.0, 95% confidence interval 1.0-4.2), an increased risk of painful defecation, a lower number of stools per week, and lower parental satisfaction. Adverse events were similar in both groups.Conclusions:To achieve treatment success, both tested doses of PEG were equally safe and effective in the treatment of children with functional constipation.