Some patients with idiopathic Parkinson's disease experience hallucinations as a result of treatment with levodopa and dopamine agonists. There is evidence for some heterogeneity in these hallucinating patients based on duration of Parkinson's disease at onset of hallucinations. We compared the frequency of polymorphisms in the dopamine D2and D3receptor genes between patients with drug-induced hallucinations and non-hallucinating patients. Two polymorphisms close toDRD2and one inDRD3were studied. No association was found with the whole group of hallucinating patients and their controls. However, an association was found with late-onset hallucinations and theCallele of theTaqIA polymorphism, 10.5 kb 3′ toDRD2. This polymorphism may be in linkage disequilibrium with a mutation inDRD2or a nearby gene that predisposes to drug-induced hallucinations which occur later in the course of idiopathic Parkinson's disease.