Neonatal hyperammonemia is a medical emergency requiring a multidisciplinary teamwork for early recognition and early treatment. The causes of neonatal hyperammonemia vary. The transient hyperammonemia of the neonate (THAN) occurs mostly in premature babies, and the prognosis is usually better than for urea cycle disorders. Here we present a near-term premature male infant with THAN. He exhibited the symptoms during the first 36 hours of life and survived after continuous arteriovenous hemodiafiltration (CAVHD). Nutritional support and sodium benzoate were also given. The diagnosis was based on laboratory tests. Long-term follow-up of neurodevelopment was suggested.