Catechol-O-methyltransferase (COMT) gene has long been implicated to play a role in the pathogenesis of schizophrenia. The aim of this study is to assess the relationship of schizophrenia and its subgroups with COMT gene polymorphism. We have attempted to evaluate a possible correlation between the severity and prognosis of the illness (the psy- chopathology of symptoms) and COMT gene polymorphisms. The study comprised 129 unrelated subjects who strictly met DSM-IV criteria for schizophrenia, and 65 healthy unrelated controls. All subjects were of Turkish origin. A clinical evaluation of all patients was accomplished by applying the Brief Psychiatric Rating Scale (BPRS) test. The analysis of COMT polymorphism was performed using the polymerase chain reaction technique. Regarding COMT gene polymorphisms, no statistically significant difference was found between schizophrenic patients and control subjects. However, within the schizophrenic group, the average of BPRS points of patients with the L
L genotype was significantly higher than those of the L
H and H
H genotypes ( F6.25, degrees of freedom2, P0.003). Although no statistically significant difference was found between the duration of illness and COMT variations, a higher frequency of hospitaliza- tion was found in patients with the L
L genotype compared with other groups ( t3.048, P0.003). In conclusion, the findings indicate that COMT gene polymorphisms were not statistically significant between patient and control groups. However, the patients with the L
L genotype may have much more severe clinical signs in Turkish schizophrenics. COMT variations, however, do not help to evaluate the susceptibility of the patients, but can help in the estimation of severity of clinical manifestations. Further studies are required to better understand the association of symptomatology of schizophrenia and other psychiatric disorders with COMT gene polymorphism.