To determine if there is a relationship between low serum ferritin and sleep disturbance in children with autism spectrum disorder, an 8-week open-label treatment trial with oral iron supplementation was conducted as a pilot study. At baseline and posttreatment visits, parents completed a Sleep Disturbance Scale for Children and a Food Record. Blood samples were obtained. Thirty-three children completed the study. Seventy-seven percent had restless sleep at baseline, which improved significantly with iron therapy, suggesting a relationship between sleep disturbance and iron deficiency in children with autism spectrum disorder. Sixty-nine percent of preschoolers and 35% of school-aged children had insufficient dietary iron intake. Mean ferritin increased significantly (16 microg/L to 29 microg/L), as did mean corpuscular volume and hemoglobin, suggesting that low ferritin in this patient group resulted from insufficient iron intake. Similar prevalence of low ferritin at school age as preschool age indicates that children with autism spectrum disorder require ongoing screening for iron deficiency.