The relative abundance of serotonin type 6 receptors (5-HT6) in some limbic regions and the high affinity of some antipsychotics to 5-HT6 receptors suggest that they might be involved in the pathogenesis of schizophrenic disorders. In a population-based association study, we tested the hypothesis that the allelic variant, C267T, of the human 5-HT6 gene confers susceptibility to schizophrenic disorders and associated aggressive behavior. We genotyped 5-HT6 receptors in 186 patients with schizophrenic disorders and 163 controls. The results demonstrated no significant difference in genotype or allele frequencies between patients with or without aggressive behaviors. However, genotype distribution was significantly different between schizophrenic patients and control subjects. This suggests that the 5-HT6 gene may play a role in the pathogenesis of schizophrenic disorders.