An 18-month-old infant presented with hypotonia, motor delay, hepatosplenomegaly, rickets and steatorrhoea. Biochemical investigations revealed typical features of Niemann-Pick disease type C. In addition, there was evidence of defective peroxisomal beta-oxidation of branched-chain substrates (3 alpha, 7 alpha, 12 alpha-trihydroxycholestanoic acid and pristanic acid). The steatorrhoea and fat-soluble vitamin malabsorption responded well to bile acid therapy. Possible causes for the double defect are considered.