Through the use of several tests of cognition we have documented sex differences in young children, adolescents, and adults on tasks that rely on the integrity of the orbital prefrontal cortex. In children under three years of age, males performed with significantly fewer errors than did females on tests of object reversals. No significant sex differences were found in older children, despite the use of a more challenging object reversal task. Sex differences were also found in adolescents and adults on the Iowa Gambling Task. On this decision-making task, in contrast to males, females appear to be responding to different elements of the task. Discussion of the implications for these findings is presented.