The ring chromosome 20 syndrome is characterized by treatment resistant non-convulsive status epilepticus, and slow waves intercalated by spikes/spike waves predominantly in the front-temporal regions. Here, we describe the case of an 18 year old patient, whose seizures began at the age of 10, these being resistant to treatment. Neurologic examination and cranial MRI were normal. Interictal EEG showed normal background activity with burst of 2-20 seconds with bilateral spike wave. Ictal EEG showed continuous paroxysmal activity with generalized spike waves discharges and slow delta waves, coinciding with nonconvulsive status epilepticus. After 1 mg of intravenous clonazepam, both clinical semiology and EEG abnormalities disappeared. A cytogenetic study showed ring chromosome 20 in 35 % of metaphases. The epilepsy associated with ring chromosome 20 constitutes a syndrome with its distinctive electroclinical characteristics.