Possible involvement of serotonergic (5-hydroxytryptamine: 5-HT) receptors in the pathophysiology of tardive dyskinesia (TD) has been suggested. In the present study, the relationship between the 5-HT(6) receptor gene (HTR6) polymorphisms and TD was studied in 173 Japanese patients with schizophrenia. The 267C/T allele of HTR6 was genotyped using PCR amplification followed by endonuclease digestion. The patients with the three 267C/T genotypes showed no significant difference in gender, age, duration of illness, or current antipsychotic dose. In addition, there were no significant differences in total AIMS scores among patients with the three genotypes. Moreover, no significant differences in genotypes and allele frequencies were observed between subjects with and without TD. These results suggest that the 267C/T polymorphism of HTR6 does not confer increased susceptibility to TD.