Two sisters, aged 38 and 32, suffering from cerebrotendinous xanthomatosis are described. The most important clinical findings were xanthomas, central nervous affection with motor and mental dysfunction, EEG changes and juvenile cataract. The diagnosis was established by the demonstration of increased amounts of cholestanol in serum. Both sisters had amenorrhea, and their excretion of dehydroepiandrosterone in the urine was increased. In the elder sister, the levels of urinary 17-keto steroids, androsterone and estradiol were also increased. Other unusual features of the disease in the elder sister were hyper-prebeta-lipoproteinemia and serum cholesterol in the higher normal range.