AIM: To assess the muscle mass of patients with inflammatory bowel disease (IBD) using ultrasound. MATERIALS AND METHODS: 102 IBD patients hospitalized in gastroenterology department of Republican Clinical Hospital (Kazan) were involved in the study. Among them, 49% of patients with ulcerative colitis, 51% with Crohn's disease, 10 people made up the control group (CG). The median age in the IBD group was 39.5 [28.5; 50] years, in the CG - 37 [26; 38] years. There were 52 (51%) women in the IBD group and 5 (50%) in the CG group. Patients were examined to assess body mass index (BMI), mid-upper arm circumference (MUAC, cm) and mid-thigh circumference (MTC, cm) of the dominant side; bioimpedance analysis of body composition using the ABC-02 "MEDASS" device; ultrasound examination of muscle thickness at two points on the leading side: ultrasound thickness of the middle of the shoulder (US-MUAC), ultrasound thickness of the middle of the thigh (US-MTC), dynamometry using a wrist dynamometer, assessment of nutritional status. RESULTS: According to BMI, patients were distributed as follows: normal in 57 (55.9%) patients; deficiency - in 12 (11.8%); overweight - 25 (24.5%); obesity - 8 (7.8%). Median MUAC in women with IBD was 28 [24.9; 31] cm, in CG - 28 [27; 28.5] cm (p>0.05); in men with IBD 29.8 [27; 32] cm, in CG - 33 [31; 34] cm (p<0.05). The median MTC in women with IBD was 54.25 [48.15; 58.10] cm, in CG - 61.5 [56; 67] cm (p<0.05); in men with IBD 48 [46; 51.4] cm, in GC - 54 [53; 54] cm (p<0.05). The median US-MUAC in women with IBD was 19.60 [18.23; 22.84] mm, CG 22.49 [20.41; 22.66] (p>0.05); in men with IBD 26.45 [22.87; 29.24] mm, in CG 21.54 [21.18; 25.13] mm (p>0.05). Median US-MTC in women with IBD was 31.05 [23.21; 37.11] mm, CG 41.30 [35.55; 41.74] mm (p<0.05), in men with IBD 30.90 [25.64; 39.99] mm, in CG 40.67 [39.10; 41.84] (p<0.05). According to the results of bioimpedansometry, the skeletal muscle mass index (SMI) was low in 32% of patients, normal in 65%, and above normal in 3%. US-MUAC correlated with MUAC (r=0.557; p<0.05), with BMI (r=0.448; p<0.05), with SMI (r=0.666; p<0.05). US-MTC correlated with MTC (r=0.505; p<0.05), with BMI (r=0.376; p<0.05), with SMI (r=0.373; p<0.05). CONCLUSION: In patients with IBD, MTC was lower than in CG. US-MTC in women and men with IBD was lower than in CG, which correlated with MTC, BMI, skeletal muscle mass according to bioimpedance measurements and grip strength according to dynamometry.