To determine whether a gluten-free diet (GFD) compared with a gluten-containing diet (GD) influences functioning of children with autism spectrum disorders (ASD), we performed a randomized, controlled, single-blinded trial. Sixty-six children (36-69 months) with ASD, within the normal IQ (> 70) range, who had been on a GFD for at least 8 weeks before enrollment were eligible for inclusion. After an 8-week run-in period on a GFD, the GFD group continued this diet and the GD group consumed at least one normal meal containing gluten per day for 6 months. There were no differences between groups in autistic symptoms, maladaptive behaviors, or intellectual abilities after the intervention. A GFD compared with a GD did not affect functioning of children with ASD.