Introduction. The current knowledge of significance of some neurobiological and clinical variables for the development of cognitive deterioration in patients with epilepsy remains sparse and controversial.Aim. The current study has been carried out in order to elucidate the role of handedness in terms of influence on cognitive processing and intelligence in patients with epilepsy.Material and methods. One hundred and thirty two patients (62 males, 70 females, aged 27.8 ± 8.9 years) with epilepsy participated in the study. Patients were divided into two groups. The first group included 112 patients that were characterized by intelligence and cognitive impairment while the second group (20 patients) had no mental deterioration and was regarded as controls. The two diagnostic categories accorded with ICD-10 criteria. The diagnosis of Dementia (F-02.8) was confirmed in 54 patients, while the diagnosis of Mild Cognitive Impairment (F-06.7) was confirmed in 58 patients.Results. Our results show that the level of left-handers among patients with cognitive Impairment achieved 14.2%, whilst in the group without cognitive deterioration there were no left-handers, and this difference was statistically significant (p = 0.051). An analysis of possible influence of motor lateralization on degree of cognitive deterioration, revealed that left-handedness determines the higher degrees of intelligence deterioration compared with right-handedness (χ2 = 6.64; p < 0,05). These data were confirmed by use of Wechsler Adult Intelligence Scale (WAIS) and the Mini Mental State Examination (MMSE) tests, and all left-handed epilepsy patients achieved lower scores on MMSE, total WAIS, as well as verbal and nonverbal WAIS scores.Conclusion. Our data confirm a role of some neurobiological variables, with emphasis on cerebral motor lateralization, in their influence upon intelligence level and cognitive deterioration in epilepsy. These data may be used for predictive purposes of intelligence assessment in patients with epilepsy.