Six cases of epilepsy associated with ring chromosome 20 are presented. The study of these cases and 20 cases reported in the literature revealed that they constitute a distinct epileptic syndrome: frequent seizures consisting of a prolonged confusional state, with or without additional motor seizures, and an ictal EEG pattern of long-lasting bilateral paroxysmal high-voltage slow waves with occasional spikes. Neurological examination results were normal, and neuroimaging studies often failed to disclose a brain lesion. The seizures were resistant to antiepileptic drug therapy. Comparison of the electroclinical features of nonconvulsive status epilepticus in six patients with and four patients without ring chromosome 20 revealed that the group with the chromosomal anomaly had more frequent, comparatively brief episodes of confusion associated with a less prominent spike component on the EEG. We propose that epilepsy associated with ring chromosome 20 constitutes a new syndrome that may provide an opportunity to scrutinize a genetic mechanism of epilepsy.