Familial hypobetalipoproteinaemia complicated by cerebellar ataxia and steatocystoma multiplex. A 55-year-old man with cerebellar ataxia and steatocystoma multiplex was found to have reduced serum concentrations of total cholesterol, betalipoprotein and apolipoprotein B. Computed tomography revealed atrophy of the cerebellum and brain stem. Of the six family members examined, four had hypobetalipoproteinaemia, and one had mild ataxia. Similar skin lesions were noted in five male relatives. This case represents a rare combination of familial hypobetalipoproteinaemia, cerebellar ataxia and steatocystoma multiplex. 