The value of tumor necrosis factor alpha (TNFα) and the polymorphism of its gene rs1800629 for development of type 2 diabetes mellitus (DM) has been shown in some studies but the mechanism of this effect and its role in some ethnic populations of patients is not fully understood. Objective — to determine the value of TNFα and the polymorphism of its gene rs1800629 in mechanisms of vascular complications development in type 2 diabetes. Materials and methods. The study involved data from 152 Ukrainian patients with type 2 DM, aged 34—80 years (53.9 ± 8.4 years) and 95 healthy persons (control). According to the results of clinical and laboratory examinations, the presence of complications was determined and the stage of the disease was established. The blood level of TNFα was determined by the immunoenzyme method (Bender Medsystems, Austria); polymorphism rs1800629 — by real time polymerase chain reaction (TaqMan Mutation Detection Assays Life-Technology, USA). Statistical data processing was performed by Statistica 10 (StatSoft, Inc., USA). Results and discussion. The blood level of TNFα in type 2 DM significantly increased in accordance with the severity of the disease (the maximum in the third stage — 7.1 times; p = 3.2e-17), which influenced the development of retinopathy (β = 0.012; p = 0.049), nephropathy by glomerular filtration rate (β = 0.011; p = 0.007) and arterial hypertension (β = 0.007; p = 0.042); the maximum was the effect on the development of macroangiopathy of the lower extremities (β = 0.033; p < 0.001). Minor allele A rs1800629 increased (OR = 1.71; 95 % CI 1.11-2.65; p = 0.015) risk of type 2 DM. For genotypes the connection with the disease is confirmed by the dominant model of inheritance (G/G versus G/A+A/A; OR = 1.87; 95 % CI 1.10-3.18; p = 0.020). Allele A contributed to decrease ofglomerular filtration rate and was associated with nephropathy (χ2 = 6.38; p = 0.041). This could be due to higher TNFα levels in G/A genotypes-carriers (1.2 times) and A/A (1.7 fold) compared to genotype G/G-carriers (p < 0.001). Conclusion. The presence of allele A rs1800629 was an important factor in the diabetic nephropathy development; one of the mechanisms of the vascular diabetic complications development was excessive expression of the TNFα gene, resulting in excessive synthesis of TNFα.