It has been recently shown that dysregulation of transforming growth factor-beta1 (TGF-beta1), IL-23 and IL-17 has been identified as a major factor involved in autoimmune disorders. Based on the increasing evidence of immune dysfunction in autism the aim of this study was to measure serum levels of TGF-beta1, IL-23 and IL-17 in relation to the degree of the severity of autism. Serum TGF-beta1, IL-23 and IL-17 were measured by Enzyme-linked Immunosorbent Assay technique in 50 autistic children aged 6-12 years, in comparison to 50 developmental disabilities and 50 typically developing-matched children. The severity of autism was assessed by using the Childhood Autism Rating Scale. We found that TGF-beta1 and IL-23 levels were significantly decreased in the plasma of children with ASD in comparison to control groups (P less than 0.0001 for both) with no significant difference in IL-17 levels. There was no correlation between IL-23 and TGF-beta1 with IL-17 in children with ASD. There was a negative correlation between TGF-beta1, IL-23 and IL-17 with the severity of autism (P less than 0.0001, 0.0001, 0.005 respectively). Our results support the findings that immune dysfunction may occur in some children with autism. (Contains 3 tables.)