One of the most challenging problems in clinical psychiatry are inter-individual differences in clinical response to antipsychotic treatment. Several studies were investigating the impact of the polymorphic cytochrome P450 2D6 gene (CYP 2D6) on the psychopathological and extrapyramidal symptoms, but the results were conflicting. There is a lack of clinical studies of the impact of CYP2D6 polymorphism on therapeutic efficacy, especially in the long-term treatment of schizophrenia. The aim of the presentation was to evaluate the impact of CYP2D6 genotype on psychopathological and extrapyramidal symptoms in a group of Slovenian outpatients with schizophrenia or schizoaffective disorder in stable remission, who were receiving long-term maintenance therapy.