THE NOSOLOGICAL definition of diffuse sudanophilic cerebral sclerosis has had a long and confused history. In 1956 Poser and van Bogaert 1 reached, on morphological grounds, the conclusion that the eponymic entity commonly termed consisted of three kinds of conditions: (1) Schilder's cerebral sclerosis, a disease closely resembling, if not identical with, multiple sclerosis; (2) The leukodystrophies, a group of heredodegenerative diseases, related to metabolic disorders such as the lipidoses and glycogenoses 2,3 ; and (3) Examples of subacute encephalitis, including Dawson's inclusion body encephalitis, van Bogaert's subacute sclerosing leukoencephalitis, and Pette-Doring's nodular pancephalitis. The exclusion of Schilder's disease and its transitional forms to multiple sclerosis from the complex group of the leukodystrophies was endorsed by Norman. 4 In the latter group, however, there remained a heterogeneous collection of sporadic and familial cases in which the demyelinative process, though having the morphological features of a leukodystrophy, was characterized