Laboratory work has confirmed that general anesthetics cause increased neuronal apoptosis and changes to the morphology of dendritic spines in the developing brains of animals. It is an effect seen with most volatile anesthetics as well as with ketamine and propofol. The effects are dose dependent and seen over particular periods of early development. There is some evidence that rodents exposed to anesthesia during infancy have delayed neurobehavioral development. There are inherent limitations in translating the preclinical data to human practice but the data cannot be ignored. Some human clinical studies have found evidence for an association between major surgery and changes in neurobehavioral outcome, although the evidence is less clear for minor surgery. These associations are certainly at least partly because of factors apart from anesthesia, such as coexisting pathology or the effect of surgery itself. Other clinical studies have found no evidence for an association between surgery and outcome. These studies are also not without limitations. Thus it remains unclear what role anesthesia exposure in infancy actually plays in determining neurobehavioral outcome. To date studies can neither confirm that anesthesia plays a role nor rule it out.