A relationship was found between the presence or absence of psychotic disorders (the study group and the control group in total n = 601) and the polymorphism of the DRD4 Ex3 genotype (s/l 0.25 vs. s/l 0.34, s/s 0.72 vs. s/s 0.59, l/l 0.03 vs. l/l 0.07, χ2 = 7.19, p = 0.027) and the frequency of DRD4 Ex3 alleles (s 0.84 vs. s 0.76, l 0.16 vs. l 0.24, χ2 = 7.72, p = 0.006). This evidence concerns the gene DRD4 and psychotic disorder.