A 9-year-old girl was referred to our hospital after recurrent episodes of hypoglycemia, altered consciousness and persistent vomiting without acetonemia or myopathic symptoms. Other pertinent laboratory data included elevated BUN, hyperammonemia and very low levels of triglycerides with elevated free fatty acids. The patient was born from unaffected but related parents (second cousins) and the illness was previously diagnosed as Reye encephalopathy. Recurrence of similar attacks suggested an underlying metabolic disorder. Several syndromes of impaired FFA beta oxidation were taken into account and discarded successively after laboratory investigations: systemic carnitine deficiency, Medium and Long Chain Acyl-CoA Dehydrogenase deficiency and Multiple Acyl CoA Dehydrogenation deficiency (Glutaric aciduria, Ethylmalonic-adipic aciduria and riboflavin-responsive multiple acyl CoA dehydrogenation deficiency). Urinary and hematic gas-chromatography and Mass-Spectrometry show no abnormality in Medium Chain fatty acids and in C6-C10 dicarboxylic acids. Carnitine plasma concentrations (both total and free) were above normal levels while in urine acetyl carnitine was low in respect to longer acyclic radicals. Among metabolic defects located at the level of hepatic fatty acid oxidation, only Carnitine Transferase deficiency can explain this peculiar mosaic of data (precursors of the blocked reaction are elevated in blood whereas lack of the metabolites derived uniquely from this reaction explains all the clinical manifestations).