5-HT2C receptor gene is viewed as an important candidate gene in pharmacogenetic studies of antipsychotic drug-induced weight gain. However, inconsistent results have been obtained in different populations. We investigated the association between the -759C/T polymorphism of the 5-HT2C receptor gene with early phase (after 4 weeks of treatment) weight gain induced by antipsychotic treatment in Korean schizophrenia patients. The study subjects were eighty-four in-patients receiving monotherapy with one of six antipsychotic drugs. Patients with the variant allele (-759T) were found to be less likely to have substantial (> 5%) weight gain (Fisher's exact test, p=0.030), and this association (t=1.91, df=75, p=0.030) was supported by the repeated measures analysis after controlling for possible confounding effects, i.e., age, sex, baseline BMI, and the type of antipsychotic medicine administered. The variant allele also appeared to have a protective effect against weight gain in a subgroup of patients receiving risperidone. These results support the involvement of the -759C/T polymorphism of the 5-HT2C receptor gene in antipsychotics-induced weight gain in the Korean population.