Research findings on the effects of raised lead levels on children's cognitive and behavioural functioning are reviewed. The results are considered separately with respect to clinic-type studies of children with high lead levels, studies of mentally retarded or behaviourally deviant children, chelation studies, smelter studies, and general population studies of dental lead. It is concluded that, although the findings are somewhat contradictory, the evidence suggests that persistently raised blood levels in the range above 40 microgram/100 ml may cause slight cognitive impairment (a reduction of one to five points on average) and less certainly may increase the risk of behavioural difficulties. There are pointers that there may also be psychological risks with lead levels below 40 microgram/100 ml, but the evidence on this point is inconclusive so far. Parallels are drawn with studies of other brain traumata and some suggestions are made with respect to both practical implications and the needs for further research.