Although the etiology of aggression is multifactorial, many studies have associated the Val158Met polymorphism of the COMT with aggression in schizophrenia. This study tests the hypothesis that Met/Met patients display more episodes of aggression and violent behaviour than Val/Val patients in a 6 year follow-up cohort of subjects with schizophrenia in contact with the South-Verona Community-based Mental Health Service. Out of the 141 subjects with an ICD-10 SCAN-confirmed diagnosis of schizophrenia, 115 completed both baseline and follow-up assessments (81.6% of the baseline cohort). Of these, 80 subjects (70%) were genotyped and rated for aggression using the Overt Aggression Scale.Met/Met homozygous patients had higher aggressive behaviour compared to Val/Val homozygous subjects. Antipsychotic dosage, alcohol and drug abuse were taken into account as confounders. The Met/Met genotype of COMT may have an effect on aggressive behaviour in schizophrenia because norepinephrine is less effectively inactivated.