Severely constipated children with encopresis in whom outpatient management has failed frequently require several days of hospitalization, as well as conventional treatments involving cathartics and enemas. A balanced electrolyte solution of the nonabsorbable polymer polyethylene glycol (GoLytely, Braintree [Mass] Laboratories Inc) offers a safe and efficient method for clearing the intestine. Twenty-four patients with a mean age of 8.1 years (range, 0.8 to 17.6 years) and an average weight of 31.5 kg received polyethylene glycol-electrolyte solution: eight patients with encopresis were given it as treatment for severe fecal retention unresponsive to outpatient management; the other 16 were being prepared for colonoscopy. Weight, complete blood cell count, and serum electrolyte, serum urea nitrogen, and serum creatinine levels were measured before solution administration and two hours afterward. Abdominal roentgenograms were obtained from the encopretic patients. The two groups were comparable in age and weight. Polyethylene glycol-electrolyte solution was given at a rate of 14 to 40 mL/kg/h until clear fluid was excreted through the rectum. Intestines were cleaned out successfully in all patients, and side effects were minimal. Children with encopresis required an average of 11.8 L (574 mL/kg) given over 22.5 hours, while the other children needed only 4.0 L (128 mL/kg) given over 7.5 hours. Weight and serum electrolyte and creatinine levels did not change significantly in any patient. The hematocrit decreased only in encopretic patients (0.38 to 0.36 [37.6% to 35.8%]) and the serum urea nitrogen level decreased in the patients undergoing colonoscopy (3.6 to 2.0 mmol/L [10 to 8 mg/dL]).