Background Constipation can lead to serious health issues and death. This systematic review summarises international research pertaining to the prevalence of constipation in people with intellectual disability. Method Studies published from 1990 to January 2016 were identified using Medline, Cinahl, PsycINFO, Web of Science, email requests, and cross-citations. Studies were reviewed narratively. Results 31 studies were identified. Constipation rates of 50% or more were reported in 14 studies; 21 studies reported rates over 33%. Based on the most representative study, over 25% of people with intellectual disability received a repeat prescription for laxatives in one year, compared to 0.1% of people without intellectual disability. Constipation was more common in those with cerebral palsy and profound intellectual disability, and associated with immobility but not age. Conclusion Constipation is a significant issue for people with intellectual disability across the life course and should be actively considered as a diagnosis in this population.