The DRD2 Ser311Cys polymorphism was studied in a sample which included 366 patients with schizophrenia and 387 healthy controls. The frequency of the Cys allele was significantly higher (p<0,009) in the group of patients compared to the controls (8,5% and 3,9%, respectively). Sustained attention assessed by P300 parameters was studied in 66 patients with the SerSer and SerCys genotypes (the CysCys genotype was not observed in the sample studied). A significant effect (p=0,01) of the SerCys genotype on P300 latency in frontal, central and temporal regions was found. Patients with the at-risk allele presented delayed latencies that reflected the lower speed of mental processes related to activation of attention resources. In conclusion, our data support the evidence of association between the Cys allele and schizophrenia obtained earlier for other populations and revealed that carriers of the genotype containing the at-risk allele had delayed P300 latencies.