In contrast to the great number of clinical and pathologic reports on the infantile (Tay-Sachs) type of amaurotic family idiocy, reports on the juvenile and especially the so-called late infantile (Bielschowsky) types are scarce. This is most likely due to the fact that the last two varieties are rare and do not present such a clear cut clinical picture as the classic form of Tay-Sachs disease. For this reason also they are usually not recognized by clinicians but are accidental observations postmortem. Described first by Jansky,1cases of the late infantile variety of amaurotic family idiocy have been recorded by Schob,2Brodmann3and Marinesco,4and have been especially well studied by Bielschowsky.5The case here recorded is remarkable not only for its pathologic but also for its clinical features, which were those of decerebrate rigidity, and for the fact that the disease occurred in one