We report here an infant with 18q deletion syndrome, and intractable apneic seizures. He had intrauterine growth retardation and dysmorphic features. Chromosomal analysis demonstrated mosaicism of 18q interstitial deletion (q12.3-q22.3). From the age of 3 months, apneic attacks occurred from once a week to over 10 times a day despite many oral antiepileptic agents, and were diagnosed as complex partial seizures. Ictal electroencephalogram and 18F-fluorodeoxyglucose-positron emission tomography at the age of 10 months identified the epileptic focus in the right parieto-temporal region. He also had severe psychomotor retardation. Head MRI examination revealed diffuse cerebral atrophy and severe white matter dysmyelination, which was caused by the deletion of myelin basic protein gene at the locus of 18q22.3. This locus may be responsible for the clinical manifestations of 18q deletion syndrome. Detailed description of the onset, seizure types, and prognosis of epilepsy associated with 18q deletion syndrome is rare. It was suggested that the locus of 18q21.3-q22.3 was responsible for autonomic seizures in 18q deletion syndrome.