The main objective of the present study was to determine the relationship between treatment responses of delirium and genetic polymorphisms in the dopamine transporter. The optimal dosages of haloperidol and risperidone in the treatment of delirium were also investigated. Either haloperidol or risperidone was administered to delirium patients, and delirium symptoms were measured daily until remission. Variable number of tandem repeat (VNTR) polymorphisms of the dopamine transporter were determined using the polymerase chain reaction. Among 42 subjects, symptoms of delirium appeared a mean of 9.68 days after hospitalization. A majority of the subjects (83.3%) had the type 10/10 polymorphism. Dosages of haloperidol and risperidone at the day of recovery were 1.67 mg/day (SD = 1.32; range 0.5-2.5 mg/day) and 1.19 mg/day (SD = 1.14; range 0.5-5.0 mg/day), respectively. The mean drug response time was 8.5 days in the haloperidol group and 4.8 days in the risperidone group (no significant difference). The response rates at the 3rd and 7th days after medication did not differ with either the drug group or the dopamine transporter polymorphism. Relatively low doses of risperidone and haloperidol exhibited similar efficacies, and dopamine transporter polymorphisms do not appear to play a major role in the action of antipsychotics on delirium.