This revised application proposes a pilot multicenter randomized placebo-controlled clinical trial of levodopa in children with ADHD both with and without periodic limb movements of sleep (PLMS) and restless legs syndrome (RLS). Both of these conditions may involve abnormalities of dopaminergic neurotransmission, and the proposal presents evidence that children with ADHD have a high rate of PLMS/RLS. PLMS/RLS is known to respond to dopaminergic medications, including levodopa, but there is only anecdotal evidence that these medications help ADHD. ADHD is a common childhood problem for which alternative medications to stimulants are needed. Although this trial may not be powered to detect small differences between groups, the goal is to look for trends to assess whether a large multicenter trial is warranted.