Aim of the study: To compare the serum levels of IL-12 and IL-23 between healthy volunteers and patients with multiple sclerosis with regard to their cognitive function. Materials and methods: A total of 21 patients with multiple sclerosis and 21 healthy individuals were enrolled into the study. The individuals were age- and sex-matched. Each participant was evaluated using the Montreal Cognitive Assessment (MoCA), the Beck Depression Inventory (BDI), and the Pittsburgh Sleep Quality Index (PSQI). The enzyme-linked immunosorbent assay was performed to assess the serum levels of IL-12 and IL-23. Results: The concentration of IL-12 was 1.61 ± 4.61 pg/mL in the group of patients with multiple sclerosis and 1.78 ± 3.54 pg/mL in the control group, p = 0.5009. The concentration of IL-23 was 19.04 ± 75.50 pg/mL in the study group and 5.50 ± 14.4 pg/mL in the control group, p = 0.5170. A significant difference was found between the control and study groups in the MoCA cognitive test (28 vs. 24 points, respectively, p < 0.0001). There was no significant difference in the Beck Depression Inventory and PSQI between the control and study groups. No significant correlations were found between the IL-12/IL-23 serum levels and psychological evaluations. Conclusions and clinical implications: The results obtained indicate that IL-12 and IL-23 may not play a role in the development of cognitive impairment. The assessment of cognitive impairment in patients with multiple sclerosis may have a screening value in preventing their cognitive deterioration.