Low level lead exposure, at levels currently found in significant numbers of children in the U.S., has been associated with decreases in IQ and other cognitive test scores in children, as well as with decreases in developmental test scores in infants. The precise nature of the cognitive deficits is not clear. This paper reviews epidemiological and developmental neurocognitive effects of lead and addresses methodological issues that may have contributed to differences in interpretation of previous research. In an attempt to provide a rationale for the lead-related deficits reported for humans, we have reviewed studies of lead-related behavioral and electrophysiological effects seen in animals as well as findings from studies that have examined the effects of lead exposure on neurochemical subcellular and cellular mechanisms. Based on these data, future strategies are suggested for determining the possible effects of low-level lead exposure on neurocognitive functioning in children.