A polymorphism of a variable number tandem repeat (VNTR), that was recently found in the promoter region of the monoamine oxidase-A (MAOA) gene, was shown to be associated with its transcriptional activity. This study examined whether this functional polymorphism of the MAOA gene is associated with the risk of developing mood disorders in a Japanese sample of 161 patients with bipolar disorder, 98 with unipolar depression, and 258 controls. There was no significant genotypic or allelic association, suggesting that the functional VNTR polymorphism in the MAOA gene is unlikely to play a major role in the pathogenesis of bipolar disorder or unipolar depression. Furthermore, we found no association between the polymorphism and a history of suicide attempt.