Carnitine acylcarnitine translocase (CACT) deficiency (SLC25A20 gene) is a rare disease affecting mitochondrial long-chain fatty acids oxidation. Presenting symptoms are cardiomuscular, associated with hypoketotic hypoglycaemia and hyperammoniemia. Diagnosis is suspected on elevated long-chain plasma acylcarnitines (C16-C18). Despite high carbohydrate and medium-chain triglycerides diet, the prognostic remains poor. We report all patients with confirmed CACT deficiency in France as a retrospective multicenter cohort study and review previously reported cases. We included 20 patients. Consanguinity was reported in 55% of cases. Disease was revealed in neonatal period (n=15) by hypoglycaemia (n=4), cardiomyopathy (n=9), arrhythmia (n=12) or in infancy (n=1, 2 months) by sudden death; 4 were investigated for family history. CACT activity was null or <2% (n=5). Molecular investigation (n= 19) revealed homozygous nonsense (n=5), homozygous missense (n=8), or heterozygous mutations (n=6). Mortality was 80% (n=16). Patients who survived neonatal event (n=14) developed psychomotor retardation (n=5), cardiomyopathy (n=2), muscle weakness (n=2) and multiple episodes of life-threatening decompensations with severe rhabdomyolysis and hyperammoniemia. Surviving patients (n=4, age 1, 3, 4 and 11 years) had limited L-carnitine supplementation (n=4) and triheptanoin diet ,(n=2). Ketone bodies (n=6) did not appear to prevent decompensation or death. We found 45 reported cases in the literature, with a 71.1% mortality at a mean age of 7.7 months. The one receiving triheptanoin diet died from infection 2 years later. CACT deficiency remains a severe disease. Ketone bodies therapy seem ineffective in the long term while triheptanoin may represent a hopeful therapy which needs further studies