Sugar is one of the major dietary components and any relation between sugar and behavior is of major interest. We review the scientific evidence supporting or refuting the relation between sugar and behavior or cognitive function. Little evidence supports the claim that refined sugar intake significantly influences behavior or cognitive performance in children. A few children may have idiosyncratic reactions or rare allergic syndromes and may therefore respond adversely, but this has yet to be substantiated by carefully controlled research. A role for glucose in the potentiation of memory processing appears clear. Further research is required to define the clinical relevance of this role and to elucidate the mechanisms involved. Sucrose may have a sedative effect, at least in infants, but there are no substantial data suggesting that any sugar has analgesic properties.