Valproic acid (VPA)-induced encephalopathy is a rarely considered side effect, with somnolence, reduced motor activity and severe deterioration of cognitive and behavioural abilities. In accordance with the increasing clinical importance of valproate clinical symptoms, causes and possibilities of treatment are reviewed by reporting on two cases of valproate-induced encephalopathy. In comparison to VPA intoxication, which is associated to increased VPA blood levels, the mechanisms of encephalopathy may include interactions of the hepatic enzymes, a direct toxic effect on the cerebral receptors, as well as drug interactions, a paradoxical epileptogenic effect and metabolic interactions. In most cases withdrawal of VPA produces regression of the symptoms within a few days; the role of L-carnitin or citrullin supplementation in clinical treatment remains unclear.