OBJECTIVE: To determine the therapeutic effectiveness and safety of polyethylene glycol 4000 (forlax) in the treatment of constipation in children over 8 years old. METHODS: This study was designed as a randomized, positive medicine (lactulose) controlled multicenter trial. A total of 216 children with constipation from 8-18 years old from 7 hospitals across China who were matched with a uniform entry criteria were enrolled in this study. The 216 patients were randomized to receive either oral forlax (20 g/d, n=105) or lactulose (15 mL/d, n=111) for 2 weeks. The therapeutic effects, including bowel movement frequency, stool consistency, clinical complete remission rate of constipation and abdominal symptoms, and the safety of forlax and lactulose were evaluated at 1 and 2 weeks of treatment. RESULTS: The median weekly frequency of bowel movement in the forlax group increased by 4 and 5 times respectively after 1 and 2 weeks of treatment, and increased by 3 and 4 times in the lactulose group (P< 0.05). The stool consistency of the two groups was both improved significantly after treatment. The Bristol score of stool consistency of the forlax and lactulose groups were 3.41±1.11 and 3.64±1.33 respectively (P< 0.05) after 1 week of treatment, and were 4.26±0.89 and 3.63±1.33 respectively (P< 0.05) after 2 weeks of treatment. The clinical complete remission rate of constipation in the forlax and lactulose groups was 70% and 40% respectively (P< 0.05) by week 1 of treatment, and that was 72% and 41% respectively (P< 0.05) by week 2 of treatment. Abdominal pain disappeared in 75% of patients in the forlax group but in only 57% in the lactulose group by week 2 of treatment (P< 0.05). No serious adverse events happened and no abnormalities were found in laboratory tests and physical examinations in the two groups after medication. CONCLUSIONS: Forlax is safe and effective in the treatment of constipation in children over 8 years old.