Magnetic resonance imaging (MRI) has enabled the identification of neuronal migration disorders in living subjects. This represents an important achievement in the diagnosis of patients with these anomalies. At least five affected families with coexistent subcortical laminar heterotopia and lissencephaly have been reported recently. This association suggests an X-linked pattern of inheritance. In the family that we report, the mother suffered from epilepsy and the oldest daughter from epilepsy and mental retardation. Both patients showed subcortical laminar heterotopia on MRI. The youngest son presented a severe encephalopathy with early onset seizures, and was found to show lissencephaly on MRI. The other two siblings, a boy and a girl, had no neurological abnormalities. The severity of these patients' clinical symptoms were clearly related to MRI findings.