Cerebrotendinous xanthomatosis (CTX) OMIM#213700 is a rare disorder of bile acid synthesis caused by deficiency of the enzyme sterol 27-hydroxylase. It results in deficiency of bile acids and accumulation of abnormal bile alcohols and accelerated cholesterol synthesis. CTX usually presents in the second or third decade with slowly progressive neurological dysfunction, cerebellar ataxia and premature atherosclerosis. Treatment with bile acid supplementation improves but does not completely reverse the neurological signs and symptoms. However, CTX is now known to be associated with a period of neonatal cholestasis. If it is diagnosed at this point, treatment may prevent the onset of neurological problems. We present the case histories and developmental findings in two affected siblings treated from infancy. We plan to continue regular neurodevelopmental reviews.