The malformation of focal pachypolymicrogyria might be the manifestation of an X-linked recessive disorder according to the results of this study. Three siblings revealed focal pachypolymicrogyria on magnetic resonance imaging (MRI) and had a strong family history of epilepsy and mental retardation. All three siblings had the same mother; the father of Patient 1 was not related to the mother, but the father of Patients 2 and 3 was related to her. The MRI of the father of Patients 2 and 3 demonstrated focal pachypolymicrogyria. The mother's MRI was normal. In this family, epilepsy or mental retardation was found mainly in the males (Patient 3 was an exception), and they were all born to female members of this family, not male. Patient 3 was probably a homozygote with an X-linked recessive inheritance, and therefore, she demonstrated the most severe clinical findings.