The mitochondrial trifunctional protein (MTP) catalyzes the last three steps in the long- chain fatty acid β - oxidation pathway. We report herein a patient with an inherited MTP deficiency and hypoparathyroidism that were both revealed at 4 months of age. Although parathyroid function appeared to be normalized following nutritional management of the fatty acid β - oxidation defect, persistent gland dysfunction was suggested by frequent mild episodes of hypocalcaemia without increase in plasma intact parathyroid hormone (iPTH) levels during recurrent fasting- induced episodes of rhabdomyolysis and by our finding of a bilateral cataract at 5 years of age. An acute provocation test conducted to stimulate iPTH release with sodium bicarbonate infusion resulted in a subnormal rise in iPTH release, which further supported a partial hypoparathyroidism. This case is the third report of inherited MTP deficiency associated with hypoparathyroidism, thus raising the possibility of a link between these two rare disorders. The mitochondrial trifunctional protein (MTP) catalyzes the last three steps in the long-chain fatty acid β-oxidation pathway. We report herein a patient with an inherited MTP deficiency and hypoparathyroidism that were both revealed at 4 months of age. to be normalized following nutritional management of the fatty acid β - oxidation defect, persistent gland dysfunction was suggested by frequent mild episodes of hypocalcaemia without increase in plasma intact parathyroid hormone (iPTH) levels during recurrent fasting-induced episodes of rhabdomyolysis and by our finding of An acute provocation test conducted to stimulate iPTH release with sodium bicarbonate infusion resulted in a subnormal rise in iPTH release, which further supports a partial hypoparathyroidism. This case is the third report of inherited MTP deficiency associated with hypoparathyroidism, thus raising the possibility of a link between these two rare disorders.