Recently, several reports describing patients with a nonprogressive clinical course, increased signal in the cerebral white matter, and cystic changes in the anterior temporal lobes on magnetic resonance imaging (MRI) have appeared. To date, 25 patients with this very distinctive condition have been described. We report four new cases of this newly recognized entity. All have been identified primarily because of the distinctive MRI features consisting of the very unusual anterior temporal lobe cystic changes. The clinical features are characterized by severe, disabling, but nonprogressive mental and motor retardation. Magnetic resonance spectroscopy has shown increased myo-inositol and decreased N-acetylaspartate in the cerebral white matter. This is a distinctive, probably genetic, condition with characteristic neuroimaging and clinical features. In the appropriate clinical situation, the neuroimaging features are diagnostic.