To establish the contribution of family history of epilepsy to seizure onset in patients with focal cortical dysplasia (FCD).From January 1998 to January 2001, we prospectively evaluated 19 consecutive patients (10 male, 9 female) with a diagnosis of FCD based on magnetic resonance imaging. All patients and at least 1 family member were directly interviewed by the same observer after completion of a semistructured questionnaire. Initially, we classified patients into 2 groups: presence or absence of family history of epilepsy. Patients with a family history of epilepsy were subdivided into 2 groups: patients with a family history of epilepsy in first-degree relatives or multiple relatives (n=5) and patients with a family history of epilepsy in relatives who were not first-degree (n=4). Statistical analysis was performed with use of the nonparametric tests Kruskal-Wallis and Kaplan-Meier (survival analysis). P=.05 was considered statistically significant.The ages of the patients ranged from 3 to 41 years (mean, 15.6 years). All patients had similar type and extent of cortical dysgenesis. Ages at seizure onset varied from 1 month to 22 years, with a mean of 5.8 years. Nine patients had a family history of epilepsy. The mean age at the first seizure in patients with a family history of epilepsy was 2.6 years compared with 8.5 years in those with no relatives having epilepsy (P=.02). When patients with a family history of epilepsy were classified further, the mean age at first seizure was 1.9 years for patients with a family history of epilepsy in first-degree or multiple relatives and 3.9 years for patients with a family history of epilepsy in relatives who were not first-degree compared with 8.5 years for patients with no family history of epilepsy (P=.04).Our results show that a family history of epilepsy is associated with an earlier age at seizure onset in patients with FCD. Although this is a preliminary finding and a larger sample is needed to confirm these results, we believe these observations provide evidence that genetic modifiers could become an important issue in the clinical presentation of patients with dysplastic lesions.