A review of 118 cases published as Kufs' disease revealed only 50 cases, including 2 patients described herein, that fulfilled our criteria for this diagnosis. Of the other 68 cases, 16 had inadequate data for analysis, 21 had evidence of a storage disease other than Kufs' disease, 10 did not have clear evidence of any neuronal storage, and 21 had atypical clinical features considered outside the spectrum of Kufs' disease. The 50 cases accepted as Kufs' disease comprised two clinical phenotypes; progressive myoclonus epilepsy (Type A) and dementia with motor disturbances (Type B). Marked photosensitivity was a striking feature of some Type A cases, and facial dyskinesias were common amongst Type B patients. Onset was typically at around the age of 30 years. A few cases began in adolescence; these differ from the protracted juvenile form of neuronal ceroid-lipofuscinosis by the absence of visual failure. Demonstration of fingerprint profiles or granular osmiophilic deposits by electron microscopy is mandatory for definitive diagnosis. Urinary sediment dolichol levels were markedly elevated in our 2 cases. This biochemical finding confirms the relationship of Kufs' disease to the early forms of neuronal ceroid-lipofuscinosis and is consistent with our hypothesis that these diseases are due to defects in the intracellular processing of lysosomal and related membranes.