Objective : There is increasing evidence that obsessive-compulsive disorder (OCD) is a multidimensional and heterogeneous disorder mediated by a range of different factors, including genetic variation. Our aim was to investigate the possible association of OCD with monoamine oxidase-A (MAO-A) gene polymorphisms in a Korean population. Methods : Patients with OCD (N=121) and normal individuals (N=276) participated. Genomic DNA was extracted from the peripheral blood of all subjects, and genotypes were determined. Males and females were treated as separate groups because the MAO-A gene is located on the X chromosome. MAO-A genotypes and allele frequencies were compared with the Yale-Brown Obsessive-Compulsive Scale (YBOCS) factor scores of both groups. Results : Male OCD patients exhibited a higher frequency of allele 3.00 and a lower frequency of allele 4.00 than did normal male patients. Additionally, male patients with allele 4.00 scored higher for YBOCS factor 1 (obsession: hoarding ; compulsion : counting, repeating, hoarding, ordering) than did those with allele 3.00. Conclusions : The MAO-A gene may be associated with the development of OCD in males. Further study is necessary to evaluate the relationship between OCD and MAO-A genetic polymorphisms