We examined the association between the Catechol-O-methyltransferase (COMT) Val158Met polymorphism and aggressive schizophrenia. The sample included 61 aggressive schizophrenic patients as well as 104 non-aggressive patients from psychiatric hospitals and 415 healthy volunteers in South Korea. In the case-control comparisons, there was no significant association between the aggressive schizophrenic patients and the COMT Val158Met polymorphism. Looking only at the subgroup of aggressive schizophrenic patients, however, we found a dose-dependent relationship between the Met allele and verbal aggression. In this subgroup, the Met carriers showed a higher verbal aggression score than those with the Val/Val homozygote. These findings support the hypothesized moderating role of the COMT gene in the aggressive behaviour in some schizophrenic patients, though they do not support the existence of a direct association between the COMT Val158Met polymorphism and aggressive schizophrenia case status in the Korean population.