The group of progressive dementing illnesses that lack distinctive histologic features includes at least four variants: a cortical type, a thalamostriate type, a motor neuronopathy type and a Ieukogliotic type. While the clinical presentation of some cases is that of anterograde amnesia, progressive aphasia and dysexecutive syndrome are the most common initial symptom complexes. A large number of reported cases are familial, although no abnormal gene has been identified. Pathologically, these illnesses are defined by cortical, hippocampal, striatal, medial thalamic, nigral and motor nuclei cell dropout and astrogliosis. In some cases, white matter gliosis is striking. Identification of specific histological or molecular markers of at least some of these conditions will greatly advance our understanding of these specific conditions as well as dementing illnesses in general.