The clinical presentation and course of abetalipoproteinemia in two male patients, a child and an adult, are described. Apoprotein B was absent in both cases and each patient had > 50% acanthocytes present on peripheral blood smear. Family studies revealed normal lipid profiles in the parents of both patients, which is consistent with the usual autosomal recessive inheritance of this disorder. In addition to a low-fat diet, both patients have been maintained on high doses of vitamins A and E. In the adult patient, detailed evaluations over a five-year period have failed to show any progression of neurological disease while maintained on high-dose vitamins. The role of supplemental vitamins A and E in the therapy of abetalipoprotenemia is discussed.