Aim  The aim of this study was to determine the relationship between parent and child Full‐scale IQ (FSIQ) in children with epilepsy and in typically developing comparison children and to examine parent–child IQ differences by epilepsy characteristics.

Method  The study participants were 97 children (50 males, 47 females; age range 8–18y; mean age 12y 3mo, SD 3y1mo) with recent‐onset epilepsy including idiopathic generalized (n=43) and idiopathic localization‐related epilepsies (n=54); 69 healthy comparison children (38 females, 31 males; age range 8–18y; mean age 12y 8mo, SD 3y 2mo), and one biological parent per child. All participants were administered the Wechsler Abbreviated Scale of Intelligence (WASI). FSIQ was compared in children with epilepsy and typically developing children; FSIQ was compared in the parents of typically developing children and the parents of participants with epilepsy; parent–child FSIQ differences were compared between the groups.

Results  FSIQ was lower in children with epilepsy than in comparison children (p<0.001). FSIQ of parents of children with epilepsy did not differ from the FSIQ of the parents of typically developing children. Children with epilepsy had significantly lower FSIQ than their parents (p<0.001), whereas comparison children did not. The parent–child IQ difference was significantly higher in the group with epilepsy than the comparison group (p=0.043). Epilepsy characteristics were not related to parent–child IQ difference.

Interpretation  Parent–child IQ difference appears to be a marker of epilepsy impact independent of familial IQ, epilepsy syndrome, and clinical seizure features. This marker is evident early in the course of idiopathic epilepsies and can be tracked over time.