The influence of polymorphic variations of the gene encoding serotonin transporter (5-HTT) on individual characteristics of cerebral hemodynamics (detected by means of functional magnetic resonance imaging (fMRI) under conditions of the performance of the tasks of the “Stop–Signal” experimental paradigm) was studied in the work. The 5-HTT gene polymorphic variants were determined by means of allelespecific PCR with DNA isolated from the blood of subjects as a matrix. Altogether, 24 subjects (eight individuals with the LL genotype, eight with the LS genotype, and eight with the SS genotype) were studied. In the experiments, the subjects either push a button after the appearance of a target stimulus (Go condition) or suppressed already prepared movement (Stop condition). Differences associated with the genotype were observed in hemodynamic responses registered in areas of the cuneus (occipital lobe of the cerebral cortex), as well as medial frontal and inferior frontal gyri (frontal lobes of the cerebral cortex). The SS genotype carriers demonstrated a significantly larger contrast between fMRI responses under Go and Stop conditions as compared with the LL and LS genotype carriers (which can be interpreted as an index of a greater intensity of the activation processes in them and a decreased capacity for the suppression of inadequate movements). Theoretically, individuals with the SS genotype have an advantage over individuals with LL and LS genotypes when making a decision with a lack of time; however, they deal worse with situations requiring the suppression of inadequate behavioral responses.