Linear sebaceous nevus syndrome, which is the association of nevus sebaceous of Jadassohn in the midfacial area with seizure and mental deficiency, has been reported in at least 100 cases. Hemimegalencephaly is a rare malformation consisting of unilateral hypertrophy of the brain, an abnormal gyral pattern, thickened cortex, white matter abnormality, and lateral ventricular dilatation. The authors report a case of linear sebaceous nevus syndrome with hemimegalencephaly, diagnosed on the basis of clinical data and brain MRI.