The effects of antiepileptic drugs (AED) on reaction time, attention, and impulsivity in 111 epileptic children, aged 5 to 13 years, are reported from the Children’s Hospital of Los Angeles and University of Southern California School of Medicine. Higher total serum levels of AEDs correlated significantly with more impulsive errors. Carbamazepine (CBZ) monotherapy levels in 54 children were negatively correlated with simple and complex reaction times and omission errors, and positively correlated with commission errors; higher serum levels were associated with faster responses and fewer omission errors but impulsive errors on complex reaction time tests were increased. Among 73 children receiving phenobarbital monotherapy, minimal slowing of reaction times and increased omission errors were noted with higher serum levels, but changes were not significant. A number of other AEDs were included in the total drug score analysis, but none was large enough to analyze individually as monotherapy, except for phenobarbital and CBZ. [1]