Ring chromosome 20 is a rare chromosomal abnormality and a rare cause of intractable epilepsy. The most commonly accepted pathophysiological hypothesis is that the deleted regions (p13 and q13) of chromosome 20 contain important genes, and that their loss leads to the development of epilepsy with or without other clinical manifestations. The most consistent clinical feature described is epilepsy. The diagnosis is made by karyotype analysis. Since the majority of patients are mosaic, at least 100 mitoses should be examined when the diagnosis is strongly suspected. It is of note that the mosaicism is typically post-zygotic. The EEG may help in suggesting the diagnosis. Typical EEG features are seen on both the interictal and ictal EEG. Neuroimaging, including high-resolution MRI and other imaging techniques, is typically normal. Occasional cases are reported with focal abnormalities on MRI such as cortical dysplasia or focal atrophy.