Abstract
A patient with progressive multifocal leucoencephalopathy was found to have primary hypersplenism, a benign disorder of the reticuloendothelial system. He failed to respond to conventional doses of corticosteroids. The clinical and pathological manifestations of his illness are described, and the development of the histopathological changes in the nervous system is discussed. Consideration of available data on progressive multifocal leucoencephalopathy reveals a striking association with disease of the reticuloendothelial system, the significance of which is discussed in relation to aetiology and treatment.