Miller-Dieker syndrome is a multiple malformation syndrome characterized by severe lissencephaly and characteristic facial abnormalities at birth. It is associated with visible or submicroscopic deletions within chromosome 17p13.3 including PAFAH1B1 (LIS1) gene. We report a six-month-old boy who presented with spasm and generalized myoclonic seizures. The patient was born at 40 weeks' gestation to a 36-year-old woman and showed developmental delay without microcephaly or prominent facial abnormality. Magnetic resonance imaging of the brain showed a few gyrus (lissencephaly). High resolution cytogenetic analysis from peripheral blood showed a normal karyotype. However, fluorescence in situ hybridization (FISH) of the metaphase chromosome using Miller-Dieker/ILS probe (Oncor, Gaithersburg, Maryland, USA) revealed only one signal of probe, indicating a microdeletion of 17pl3.3 region including PAFAH1B1 (LIS1) gene. We suggest that FISH 17p13.3 studies should be performed in addition to a standard metaphase analysis in patients with lissencephaly even if facial anomaly is not noted. A confirmatory diagnosis using FISH would be helpful in terms of leading to allow genetic counseling and availability prenatal diagnosis to the family.