Constipation is a common problem in people with intellectual disability (ID). Laxatives are frequently prescribed with disappointing results. The prevalence of constipation was investigated in a random population of 215 people with ID (IQ < 50) and constipation was correlated with clinical symptoms. All subjects were scored for bowel habits. Constipation was defined as having a bowel movement less than three times a week or the necessity of using laxatives more than three times a week. Further possible accompanying factors were evaluated. The control subjects were defined as individuals who did not use laxatives. Subjects with constipation were defined as patients and were compared to subjects without constipation (controls). One hundred and forty-nine out of 215 cases (69.3%) showed constipation. Constipation was significantly correlated with non-ambulancy, cerebral palsy, the use of anticonvulsive medication or benzodiazepines, H2-receptor antagonists or proton pump inhibitors, food refusal, and an IQ < 35. Fifty-eight per cent of the patients used bisacodyl or magnesium oxide, 39% lactulose, 13% sodiumlaurylsulphoacetate/sodium citrate/sorbitol and only 10% were given sodium phosphate enemas. Faecal soiling was found in 15% of subjects, while manual evacuation of faeces was performed in nearly 7% of cases. Constipation was randomly demonstrated in almost 70% of the population with ID. Subjects with the above-mentioned accompanying factors are especially at risk for constipation. Contrary to the general population, constipation in people with ID is associated with little use of phosphate enemas, microlax, a low incidence of faecal soiling and manual evacuation of faeces, suggesting an aetiology without distal faecal impaction. The regimen and effect of therapy has to be studied to define adequate treatment schedules.