Valproate overdose, extensively described in adults and older children, has been reported in only 1 newborn: a 26-day-old female who developed a severe cerebral edema leading to a fatal outcome. Therefore, the consequences of valproate overdose are largely unknown in the neonatal period. Here, we present the clinical evolution of a 6-day-old newborn who developed hyperammonemic encephalopathy after the accidental administration of 310 mg/kg of oral valproate in a single dose. Despite the very high valproate and blood ammonia levels, he did not develop life-threatening complications and he completely recovered without sequels. His brain magnetic resonance imaging showed symmetric focal T1 prolonged signals in both globi pallidi that completely resolved over time, a neuroimaging pattern that was not previously described in valproate overdose. Our case report suggests that valproate overdose in newborns can be completely reversible even when the valproate and ammonium blood levels are very high.