This editorial briefly reviews the significance of lymphoid nodular hyperplasia in the intestinal tract of children with autistic spectrum disorder. The distinction between physiological and pathological lymphoid hyperplasia of the intestinal tract is of importance in the context of a possible causative link with autism. A primary intestinal lesion may occur as part of the broad spectrum of immunological disorders to which autistic children are prone. This could result in increased intestinal permeability to peptides of dietary origin which may then lead to disruption of neuroregulatory mechanisms required for normal brain development. Alternatively, there could be a primary defect in the translocation and processing of factors derived from the intestinal lumen. These possibilities deserve further investigation and should not be lost in the fog of the controversy regarding the role of measles/mumps/rubella vaccination in the aetiology of autistic spectrum disorder.