Valproate is an important but uncommon cause of drug induced parkinsonism in the elderly. The development of symptoms after valproate onset is unpredictable, and severity of symptoms is unrelated to plasma levels. However, though the majority of cases improve after drug cessation, parkinsonian symptoms can persist and should prompt investigation into underlying degenerative parkinsonism, as valproate can unmask idiopathic Parkinson's disease in susceptible individuals. This case describes a patient on chronic valproate therapy developing a severely disabling akinetic-rigid syndrome, only partially reversed on stopping valproate. We hypothesise that an increase in valproate dosage unmasked clinically silent Parkinson's disease. The patient made an excellent recovery following cessation of valproate and commencement of dopaminergic therapy.