Carnitine-acylcarnitine translocase (CACT) deficiency (McKusick 212138) is a rare life threatening disorder characterized by hypoketotic hypoglycemia, hyperammonemia, encephalopathy, cardiomyopathy hepatopathy, and myopathy. Here, we present a detailed clinical course of 3 Saudi siblings with a severe phenotype. The third patient was described in more detail. Early medical intervention in the form of 25% dextrose intravenous infusion and carnitine supplement followed by a gradual introduction of a high carbohydrate low fat special formula resulted in a good clinical and biochemical response to the treatment in our patient. However, early nephrocalcinosis, severe hypotonia, and subsequently intravascular cerebral accident could not be prevented. He died at 18 months of age as a result of metabolic decompensation. This suggests that CACT deficiency is still a lethal disorder even with an early and aggressive medical intervention.