Hyperammonemia is a characteristic feature of the urea cycle defects and organic acidemias but it may also accompany some other metabolic disorders or hepatic dysfunction. Additionally, some drugs and various toxins may cause elevated ammonia levels. A girl patient presented with vomiting and hypoglycemia attack when she was 2.5 years old. Ten years later, when she was 12.5 years old, she was admitted to the emergency department with severe vomiting attack, and then loss of consciousness totally. Laboratory investigations revealed mildly elevated liver enzymes and hyperammonemia. Free carnitine level was detected very highly elevated in tandem mass analysis. Carnitine palmitoyltransferase type 1a (CPT1a) deficiency was suggested in the patient and, molecular genetic analysis showed homozygous c.364_365dupAT pathogenic variant in the CPT1A gene. High-carbohydrate diet that is low in fat was commenced. She has no neurological sequelae. Elevated carnitin levels and hyperamonemia together with hypoketosis sh.ould be alarming for CPT1a deficiency.