The incidence of relapses of ulcerative colitis (UC) within 1 year after diagnosis of this pathology amounts to 50%. Remission persists in 25% of the patients during 3-7 years. The annual frequency of relapses is 18%. Only 50% of the patients have remission during 5 years after the first attack of UC. The objective of the present study was to compare the medium-term results of the treatment of the patients suffering a severe or moderately severe attack of ulcerative colitis by means of standard anti-inflammatory therapy or a combination of anti-inflammatory therapy with the application of a culture of bone marrow mesenchymal stem cells (MSC). Materials and methods. All the patients suffering an acute attack of ulcerative colitis (within 6 months after the onset of the disease) were divided into two groups. Group 1 was comprised of the patients having UC (n=12) who were treated with the use of the MSC culture, besides standard anti-inflammatory therapy. Group 2 contained the patients (n=10) given the standard anti-inflammatory treatment including preparations of 5-aminosalicylyc acid (5-ASA) and glucocorticosteroids (GC). The patients presenting with severe UC attacks accounted for 58.3% and 60% of their total number in groups 1 and 2 respectively and those with moderately severe attacks for 47.0% and 40%. The age of the patients in group 1 varied from 22 to 44 (mean 29) years and of those comprising group 2 ranged from 19 to 54 (mean 29) years. Groups 1 and 2 included 7 (58.3%) and 60% women respectively. The criterion for the effectiveness of the treatment of the patients suffering the first attack of ulcerative colitis was remission of the disease within 12 months after the initiation of the study. The clinical activity of UC was estimated using the scale of D. Rachmilewitz and endoscopic activity based on the Mayo scoring system. The duration of the follow-up period for individual patients varied from 36 to 40 months after the administration of the culture of bone marrow mesenchymal stem cells. Results. The initial value of the Rachmilewitz score (RS) for the patients of group 1was 9.66±0.43 and for the patients of group 2 10.1±0.52. The Mayo scores were 7.66±0.37 and 7.3±0.39 respectively (p=0.084). The relative risk (OR) of the development of UC relapse in the patients treated with the use of the MSC culture (group 1) compared with those given 5-ASA/GC (group 2) during one year was estimated at 0.3 (95% CI 0.08-1.36; p=0.2; χ2=1.47). RS was 3.33±0.54 and 4.4±1.13 in groups 1 and 2 respectively (p=0.81), the Mayo score in the patients of the same groups was 3.1±0.85 and 3.9±1.06 (p=0.66). Two years after the onset of the observations, OR was 0.31 (95% CI 0.11-0.87; p=0.03; χ2=4.58) RS was 4.1±0.96 and 6.5±1.1 (p=0.049), Mayo score 3.41±1.01 and 5.6±1.06 (p=0.038) respectively. Three years after the onset of the observations, OR was 1.67 (95% CI 0.18-15.8; p=0.086; χ2=0.03). RS was 4.75±1.13 and 8.1±1.1 (significant difference: p=0.001), but the Mayo score was not significantly different between the patients treated with the use of the two different therapeutic modalities (4.66±1.1 and 6.8±1.39 respectively; p=0.14). Conclusion. The administration of the culture of bone marrow mesenchymal stem cells to the patients presenting with ulcerative colitis enhances the effectiveness of anti-inflammatory therapy, increases the length of the period of remission, and decreases three-fold the risk of repeated attack during 2 years. However, the intermittent administration of MSC does not ensure the long-term maintenance of UC remission. Regular administration of MSC is needed the frequency of which remains to be determined.