Background Background & Aim: Differential diagnosis between Crohn's disease (CD) and ulcerative colitis (UC) could be a challenge, since the endoscopic and clinical characteristics of both may resemble. Furthermore, radiological methods do not provide complete information.To assess the possibilities of endoscopic ultrasonography (EUS, endosonography) for the differential diagnosis between ulcerative colitis (UC) and Crohn's disease (CD) in doubtful or controversial cases. Methods Methods: We examined 50 IBD patients during the active phase: CD-28 patients (M: W=16:12,average age 27.3 ± 0.7 years), UC-22 patients (M: W=8:14, average age 32 .6 ±1.7 years). The control group included 15 patients without UC or CD. All patients underwent EUS colonoscopy for measurement of wall thickness, assessment vascularization degree and compression elastography was perform. Results Results.It was found that wallthickness in CD was 5.66 ± 0.36 mm, was 1.5 times more than in UC (3.96 mm ± 0.13 mm) and 2 times more than in controls(2, 62 ± 0.11mm). Frequency of all intestinallayers in CD was noted in 68% vs 9% in UC (p < 0.02). On the contrary, in UC, wall thickening due to the mucosa and submucosa was significantly more common than in CD (82% and 7.2%, respectively, p < 0.05). Vascularizationdegree of colon wall in UC in most cases was reduced, while in CD, on the contrary, it was increased. According to elastometry, type 1 staining according to Ueno E., corresponding to the soft-elastic structure of colon wall, was detected in UC in 78% of cases, in CD in 54%. Type 2 according to Ueno E. was verified in 22% in UC, in 45% in CD, which indicates the presence of fibrosis foci in colon wall, mainly in CD patients. Conclusion Conclusion. The obtained EUS data can be as criteria for differential diagnosis between UC and CD in compound cases and clarify the presence and degree of fibrosis, for example, if strictures in CD.