We investigated the association between the tryptohan hydroxylase 1 (TPH1) gene and aggression in schizophrenia in a Korean population.The sample included 61 aggressive patients as well as 104 non-aggressive patients from psychiatric hospitals and 335 healthy volunteers in Korea. Blood samples were collected from all participants for TPH1 A218C genotyping. The patients were administered standard psychiatric interviews as well as a self-report questionnaire for anger-related traits.In the case-control phenotypic comparisons, there was no significant association between the aggressive patients and the TPH1 A218C polymorphism. There was no significant effect of the TPH1 genotype on the anger-related traits, or no significant interaction between the genotype and group (aggressive and non-aggressive patients).These findings suggest that TPH1 does not play a major role in aggressive behavior via anger in schizophrenic patients.