Objective. To assess the characteristics of the conducting pathways in the white matter in patients with types 1 and 2 diabetes mellitus (DM) with and without cognitive impairment. Materials and methods. The study involved 85 patients with type 1 diabetes mellitus and 135 with type 2 diabetes mellitus, divided into patients with normal cognitive functions and those with cognitive impairments. The groups were comparable in terms of age and disease duration. Screening for cognitive disorders was with the Montreal Cognitive Assessment (MocA). Brain MRI scans were performed using a 1.5-T instrument. Results. These studies identified a predominance of mild and moderate cognitive impairments in type 1 DM and moderate and severe in type 2 DM; impairments were apparent mainly as impairments to memory, attention, and visuospatial orientation. Between-group analysis of brain tractography studies did not identify any differences in the integrity of tracts in types 1 and 2 DM, though very significant risk factors for impaired functioning of the conducting pathways were seen: arterial hypertension (H = 6.602833, p = 0.0368), the severity of polyneuropathy (H = 15.30420, p = 0.0005), the extent of nephropathy (H = 9.993923, p = 0.0068), and the extent of retinopathy (H = 8.445891, p = 0.0376) in type 1 DM; age (H = 7.381742, p = 0.0607) in type 2 DM; the cholesterol level (H = 4.009380, p = 0.0452; H = 4.057357, p = 0.0440) in both types of DM. The corticospinal and commissural tracts were the most susceptible to damage. Conclusions. No statistically significant differences in the axial diffusion of brain tracts were seen in patients with and without cognitive impairments. However, we confirmed the most important risk factors for damage to white matter structures: arterial hypertension, complications of diabetes, cholesterol level, and age.