To study the impact of type 2 diabetes mellitus (DM2) on the severity of liver steatosis and fibrosis in patients with non-alcoholic fatty liver disease (NAFLD). To conduct a paired case-control study 2989 patients were examined at the Federal Research Center of Nutrition, Biotechnology and Food Safety. Pairs were matched by gender and age and distributed into groups: NAFLD + DM2+ (n=313), NAFLD + DM2- (n=313) and a control group of patients without NAFLD and without DM2 (n=313). The severity of liver steatosis was determined by measuring the controlled attenuation parameter. The severity of liver fibrosis was determined by measuring the liver stiffness measurement. Body composition of the patients was determined using bioimpedance measurements. Indicators of lipid and carbohydrate metabolism, and the serum activity of liver enzymes was determined by standard biochemical methods. In NAFLD + DM2+ group compared to NAFLD + DM2- group, and in NAFLDM + DM2-compared to the control group, weight, BMI, waist and hip circumference, waist-to-hip ratio were higher, while in all. In NAFLD + DM2+ and NAFLD + DM2- groups the volume of fat mass directly correlated with the level of blood triglycerides (r=0.21), HbA1с (r=0.32) and fasting blood glucose (r=0.35), and inversely correlated with high-density lipoproteins (r=-0.19). In NAFLD + DM2+ group versus NAFLD + DM2- group severe steatosis (S3, 78% versus 59.4%; p<0.001) and severe fibrosis (F4, 8% vs 2.6%; p<0.001) was more common; 70% of patients in the NAFLD + DM2- group had no liver fibrosis according to elastography (F0), while in the NAFLD + DM2+ group only 43.2% of patients had no liver fibrosis (p<0.0001). When NAFLD is accompanied by DM2, there is an increase in total fat mass, the severity of steatosis and liver fibrosis, and an associated deterioration of lipid metabolism. More than half of these patients have various stages of liver fibrosis, which indicates the progressive nature of the disease.