Medium-chain acyl-CoA deshydrogenase deficiency (MCADD) is the most frequent disorder of mitochondrial fatty acid oxidation (MFAO). We report a 3 year-old girl with enterovirus viremia who was referred after 36 hours of fasting with hypoketotic hypoglycemic coma and myolysis. Evolution was complicated by acute renal failure, increased serum levels of transaminases and hypoparathyroidism. Diagnosis of MCADD was supported by typical plasma acylcarnitine and urinary organic acid profiles, and confirmed by homozygosity for the common missense A985G mutation. Whereas myolysis is frequent in MFAO defects, it is rarely reported as a major accompanying sign in MCADD. Hypoparathyroidism has been previously reported in some MFAO deficiencies but has never been mentioned in association with MCADD. We review the possible mechanisms of hypoparathyroidism in MFAO deficiencies. Parathyroid glands and pancreas dysfunction should be screened in MFAO defects as these organs could be implicated in the clinical spectrum of the frequent A985G MCADD disease-causing mutation.