Iron deficiency has been suggested as a possible contributing cause of attention deficit hyperactivity disorder (ADHD) in children. This present study examined the effects of iron supplementation on ADHD in children. Twenty-three nonanemic children (aged 5-8 years) with serum ferritin levels <30 ng/mL who met DSM-IV criteria for ADHD were randomized (3:1 ratio) to either oral iron (ferrous sulfate, 80 mg/day, n = 18) or placebo (n = 5) for 12 weeks. There was a progressive significant decrease in the ADHD Rating Scale after 12 weeks on iron (-11.0 +/- 13.9; P < 0.008), but not on placebo (3.0 +/- 5.7; P = 0.308). Improvement on Conners' Parent Rating Scale (P = 0.055) and Conners' Teacher Rating Scale (P = 0.076) with iron supplementation therapy failed to reach significance. The mean Clinical Global Impression-Severity significantly decreased at 12 weeks (P < 0.01) with iron, without change in the placebo group. Iron supplementation (80 mg/day) appeared to improve ADHD symptoms in children with low serum ferritin levels suggesting a need for future investigations with larger controlled trials. Iron therapy was well tolerated and effectiveness is comparable to stimulants.