Familial hypobetalipoproteinaemia is a rare condition and is usually asymptomatic in heterozygotes. We report a case of hypobetalipoproteinaemia in an 8-month-old boy presenting with diarrhoea and failure to thrive since birth, who has been successfully treated with dietary restriction and large oral doses of vitamin E. This disease is one of the causes of chronic diarrhoea in childhood and its early treatment probably prevents irreversible retinal and nervous system lesions in later life.