A 24-year-old woman and a 13-year-old boy had suffered from diarrhoea, walking disorders, visual complaints and other complaints for many years. Once the suspicion of cerebrotendinous xanthomatosis (CTX) had been confirmed with biochemical and genetic tests and treatment with chenodeoxycholic acid had been started, the diarrhoea disappeared and the neurological symptoms lessened. CTX is a rare, autosomal recessive metabolic disease. The clinical hallmarks are: bilateral juvenile cataract, chronic diarrhoea, progressive neurological symptoms and signs, and tendon xanthomas. The phenotypic variability often hinders the clinical diagnosis. The biochemical diagnosis can be made by determining the serum cholestanol level and the excretion of urinary bile alcohols, followed by a mutation analysis. CTX is a treatable disease and therefore an early diagnosis is important.