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With an estimated worldwide-pooled prevalence of approx-imately 5 % in children (Polanczyk, de Lima, Horta, Biederman, & Rohde, 2007), ADHD is one of the most common child-hood neuropsychiatric conditions. According to the criteria of the Diagnostic and Statistical Manual of Mental Disorders (4th ed. text rev.; DSM-IV-TR; American Psychiatric Association [APA], 2000), ADHD is defined by a pervasive and age-inappropriate pattern of inattention, hyperactivity-impulsivity, or both. Despite an extensive worldwide literature (Wolraich, 1999), the genetic (Mick & Faraone, 2008) and environmental etiological factors (Millichap, 2008), as well as the exact pathophysiology underlying ADHD, are not well understood. Intriguing albeit preliminary observations suggest that iron deficiency may be involved in the pathophysiology of ADHD, at least in a subset of patients (Cortese et al., 2008; Konofal, Lecendreux, Arnulf, & Mouren, 2004). Iron is an essential trace metal, which plays a central role in a multi-tude of biological processes, including many essential brain functions (Andrews, 1999). The iron deficiency hypothesis of ADHD is grounded on several lines of evidence. First, iron is a cofactor of enzymes necessary for the synthe-sis and catabolism of the monoaminergic neurotrans-mitters (Youdim, 2000), which are implicated in the pathophysiology of ADHD. Second, iron deficiency is asso-ciated with decreased dopamine transporter expression (Beard, Connor, & Jones, 1993); variation in the dopamine transporter gene has been linked to genetic vulnerability for ADHD (Mick & Faraone, 2008). Third, iron deficiency may lead to dysfunction in the basal ganglia (Youdim, Ben-Shachar, & Yehuda, 1989), which are believed to play a significant role in the pathophysiology of ADHD (Biederman & Faraone, 2005). Fourth, iron deficiency has been reported in children with cognitive and behavioral impairments that prominently include poor attention and hyperactivity (Lozoff et al., 2006). Peripheral (i.e., in the body) iron status may be estimated by serum ferritin levels. To date, 14 studies assessing serum 430712 JADXXX10.1177/1087054711430712Do nfrancesco et al.Journal of Attention Disorder