The spectrum of clinical presentation of fatty acid oxidation defects (FAOD) continues to expand. One FAOD, L-3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency has been associated with liver disease in pregnancies involving a heterozygous mother carrying an affected fetus. Hepatic carnitine palmitoyltransferase (CPT I) deficiency typically presents as a Reyelike syndrome in children between 8 and 18 mo. of age. We have investigated a family in which the mother developed liver disease consistent with acute fatty liver of pregnancy (AFLP) and hyperemesis gravidarum in her two successive pregnancies. Neither child nor their mother was found to carry the common LCHAD G1528C mutation. Both children were subsequently shown to have absent activity of CPT I. This is the first report of CPT I deficiency presenting as maternal illness in pregnancy.