In two female patients of 62 and 81 years old, a metabolic encephalopathy was diagnosed which was ascribed to the use of valproic acid. Both had elevated ammonia levels in arterial blood, without hepatic failure. The first patient eventually became comatose and required artificial ventilation. After discontinuation of the valproic acid and with the aid of supportive measures, both women recovered. In patients with an impaired level of consciousness who are using valproic acid, a metabolic encephalopathy caused by this drug should be considered. Elevated levels of ammonia can be found but are not mandatory. Discontinuation of valproic acid will lead to recovery of consciousness.