Constipation is a common paediatric problem, but its prevalence in Asia is unknown. A cross-sectional survey using a previously validated, self-administered questionnaire was conducted in randomly selected children aged 10–16 years, in five randomly selected schools in Sri Lanka. Two schools were in Eastern Province, which has been affected by the separatist war. Constipation was defined using Rome III criteria. Of 2694 children included in the analysis, 416 (15.4%) had constipation. Symptoms independently associated with constipation were straining (71.6% vs 28.4% of controls), bleeding per rectum (14.2% vs 2.2%) and abdominal pain (55% vs 35.2%). The prevalence of constipation was significantly higher in those with a family history of constipation (49% vs 14.8%), living in a war affected area (18.1% vs 13.7%) and attending an urban school (16.7% vs 13.3%). In conclusion, chronic constipation is a significant problem affecting 15% of Sri Lankan school children and adolescents.