Genetic variants of the monoamine oxidase A (MAOA) have been associated with aggression-, anxiety-, and addiction-related behavior in several nonclinical and clinical populations. Here, we investigated the influence of allelic variation of MAOA activity on aggression-related personality traits and disease risk in patients with personality disorders. Personality disorders were diagnosed with the Structured Clinical Interview of DSM-IV and were allocated to cluster A, B, and C. Personality features were assessed by the revised NEO Personality Inventory and the Tridimensional Personality Questionnaire. The genotype of the MAOA gene-linked polymorphic region (MAOA-LPR) was determined in 566 patients with personality disorders and in 281 healthy controls. MAOA genotype was significantly associated with cluster B personality disorders (chi2=7.77, p=0.005, df=1) but not with cluster C personality disorders. In total, 26.0% of cluster B patients were hemi- or homozygous for the low-activity variant of the MAOA genotype, compared to 16.4% in the control group. Associations between MAOA variants and personality domains related to impulsivity and aggressiveness were inconsistent. Our findings further support the notion that allelic variation of MAOA activity contributes modestly to the balance of hyper- (impulsive-aggressive) and hyporeactive (anxious-depressive) traits.