To investigate the role of iron deficiency in general cognitive and behavioral development in post-institutionalized (PI) children during the early post-adoption period. PI children (N = 57) adopted from Eastern Europe or Central Asia (9-46 months of age) were seen at baseline around 1 month after arrival into the US and at follow-up 6 months later. Measures included anthropometry, iron status, the Toddler Behavior Assessment Questionnaire-R (TBAQ-R), the Mullen Scales of Early Learning, and examiner-rated behaviors during testing. 26 % were iron deficient at baseline; 18 % were iron deficient at follow-up. There was a trend for those with iron deficiency at baseline to be more fearful on the TBAQ-R. Those with iron deficiency at follow-up displayed more hyperactivity on both the TBAQ-R and the examiner-rated behaviors. Those with iron deficiency at follow-up were more likely to score below average on the Mullen Early Learning Composite (iron deficient: 80 %; good iron status: 32 %). The association between iron status at follow-up and the Mullen Early Learning Composite was mediated by inattention and hyperactivity behaviors during testing. Iron deficiency is associated with neurobehavioral alterations months after arrival, mediated by the effect on attention and activity levels. Iron status needs to be monitored at least through the first half-year post-adoption, particularly in children exhibiting rapid catch-up growth. Additionally, developmental evaluation is recommended in those with iron deficiency, even in children with good iron status at arrival.