Psychiatric disorders are common in Parkinson's disease (PD) and hallucinations are observed in nearly 40% of PD patients. The involvement of dopaminergic system in the pathogenesis of psychosis has been sustained by most of the authors even if several evidences indicate that multiple neurochemical substrates might underlie psychosis in PD. In PD there is an extensive loss of serotoninergic raphe neurons and serotonin dysfunction had been implicated in the pathogenesis of many psychiatric disorders such as depression, schizophrenia, and in psychosis of patients with Alzheimer disease. The association of a serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the 5-HT2A receptor T102C polymorphism with psychosis in a group of patients with PD was investigated. No significant differences in the distribution of allele and genotype frequencies of the 5-HTTLPR (p>0.01) and 5-HT2A T102C (p>0.05) were found between patients and controls as well as between the patients' subgroups without and with psychosis. These data might suggest that 5-HTTLPR and 5-HT2A polymorphisms are not major susceptibility factors of psychotic symptoms in PD patients.