Objective. To study blood cortisol level in patients with diabetic foot syndrome (DFS), to analyze the possibility of using cortisol level as a biochemical criterion of diagnosis and severity of DFS.Materials and methods. A non-randomized study was performed on 59 patients, who were divided into two groups: patients with the 3rd degree deforming arthritis of the knee joint without a history of diabetes mellitus (DM) and patients with DFS. Venous blood was collected on an empty stomach to determine the levels of cortisol, C-reactive protein, glycated hemoglobin, total protein, and hemoglobin.Results. Our data demonstrated that the blood cortisol level was statistically significantly higher (p < 0.05) and higher than normal in the experimental group of patients with DFS (701.69 (626.44; 904.63) nmol/L) when compared with the control group of patients with 3rd degree deforming knee joint arthrosis without a history of DM (423.7 (326.5; 516.20) nmol/L). Blood cortisol levels in patients with DFS decreased statistically significantly in 5 days after the treatment and was 382.26 nmol/L. Body mass index (BMI) (r = 0.946; p < 0.01) correlated with blood cortisol levels in patients with type 2 diabetes and with a complication of DFS. In patients with DFS, determination of blood cortisol content has the greatest diagnostic value as a biochemical criterion of DFS compared with other studied parameters (AUC, 0.915; p = 0.037). Cortisol content in patients with DFS gradually increases with the increase in the classification category of the University of Texas.Conclusion. Determining the level of cortisol in blood can be useful in the diagnosis of DFS, as well as to determine the degree of soft tissue damage of the lower extremities.