Background: In clients with pervasive developmental disorders (PDD), some authors have noticed the presence of gastrointestinal disorders and behavioural disorders. An augmented prevalence of different histological anomalies has also been reported. The aim of our study is to highlight the prevalence of gastrointestinal disorders in this adult with PDD sample and to demonstrate the importance of accurate evaluation of gastrointestinal disorders in clients with PDD. Methods: The present comparative study involved 118 clients. Our research was motivated by the clinical observation that behavioural disorders sometimes disappeared with administration of anti-gastric acid or anti-ulcerous medications. It focused on two samples of clients with intellectual disability--those with associated PDD and those without. The presence of gastrointestinal disorders was assessed retrospectively on the basis of hospital records. Results: The prevalence of gastrointestinal disorders reported in clinical files was 48.8 in clients with PDD, as compared with 8.0 in non-PDD clients (P less than 0.00001). Conclusion: Gastrointestinal disorders, and especially gastrooesophageal reflux, if neglected, may contribute to behavioural disorders in PDD clients. Moreover, gastrointestinal disorders may be considered as a feature of PDD. We highlight the fact that somatic disorders may coexist in persons with PDD.