To search for the origin of frontal lobe dysfunction identified by the Wisconsin card sorting test (WCST) in temporal lobe epilepsy (TLE) patients, we investigated the WCST performance among 19 children with TLE (with hippocampal atrophy (HA group N=12), without structural lesions (NSL group N=7)), 15 patients with frontal lobe epilepsy (FLE group), and age-matched normal controls (N group). The paired verbal association learning test (PVALT) and Benton visual retention test (BVRT) were also performed. HA group and FLE groups achieved significantly fewer categories and demonstrated more perseverative errors on the WCST than NSL and N groups. In addition, category achievement in WCST showed significant inverse correlation to age at the initial status convulsivus in the HA group (P<0.05). The achievement on PVALT and BVRT did not show any significant differences between HA and FLE groups (P>0.05). Thus, the frontal lobe dysfunction in the HA group is found to exist as early as 7 years old, when they seem to have only a short seizure history or to receive a little electrical interference from the temporal lobe focus to the frontal region. These facts would underscore the importance of prefrontal dysfunction persisting from the early insults and only becoming apparent after maturation of the prefrontal region in patients with mesial TLE.