The authors hypothesised that red dermographism--a skin reaction involving the cholinergic system--is more frequent in children with autism spectrum disorders (ASDs) than in children exhibiting typical development. We used a dermatological examination to study red dermographism in this transverse study, which compared forty six children with ASDs with seventy one children exhibiting typical development. Both univariate and stratified statistical analyses were performed. In comparison with the control group, children with ASDs had a greater prevalence of red dermographism, especially the subgroup of children with autism and Asperger syndrome. Our results reflect a probable difference in the functionality of the cholinergic system. Indeed, ASDs are usually considered neurodevelopmental disorders caused by several factors. Cholinergic system abnormalities may be involved in the pathophysiology of ASDs, at least for a subgroup of individuals. The implications for a possible treatment strategy and a potential biomarker for ASDs are discussed. (Contains 2 tables.)