Introduction. Ulcerative colitis (UC) and Crohn’s disease (CD) belong to the category of inflammatory bowel disease (IBD) and are one of the most pressing problems of gastroenterology worldwide, including due to the development of specific life-threatening complications. Chronic inflammation in the colon in IBD is the cause of the development of one of these complications - colorectal cancer, which requires disabling colectomies and is also one of the leading causes of death among IBD patients. In the Russian population of IBD patients the prevalence of dysplasia and cancer of the colon mucosa has not been previously studied in large epidemiological studies. The aim of the study was to assess the incidence of colorectal cancer in patients with IBD in St. Petersburg. Materials and methods. Within the framework of this publication, the results of three studies were compared: a single-center retrospective cohort study conducted on the basis of the city center of IBD in St. Petersburg (516 patients with IBD who admitted to this medical institution for the period 2020-2023); a multicenter epidemiological study aimed at assessing the clinical features of IBD among the population of St. Petersburg (1072 patients with IBD who admitted to 42 outpatient clinics and 6 city hospitals in 2018-2020); registry study based on the general statistical module of the regional IBD Register of St. Petersburg, operating on the basis of a regional fragment of the unified healthcare state information system (12,858 patients with IBD, data collection period: 2019-2022). Results. As a result of comparing data from three studies, the incidence of IBD-associated colorectal cancer in St. Petersburg was calculated, which was 15.7 cases per 10,000 patients with UC per year and 11.5 cases per 10,000 patients with CD per year. Compared to the population of St. Petersburg as a whole, the likelihood of developing colorectal cancer in patients with UC was 2.9 times higher, in patients with CD - 2.4 times higher. At the same time, in a single-center study, when assessing the prevalence of IBD-associated colorectal cancer, it was found that compared with other life-threatening complications of IBD, it was much less common: toxic dilatation of the intestine occurred 3 times more often, intestinal perforation occurred 20 times more often, decompensated bowel stricture occurred 21 times more often, and severe anemia requiring blood transfusion occurred 36 times more common. Also, as a result of a single-center study, it was found that for 1 case of IBD-associated dysplasia of the colon mucosa, there were 5 cases of sporadic dysplasia. Conclusion. The selection of the most effective therapy and systematic endoscopic examination of patients with IBD will significantly reduce the likelihood of developing colorectal cancer, and systematic observation of the patient with regular endoscopic monitoring of the colon with multifocal biopsy will allow timely detection of dysplasia of the colon mucosa in accordance with current clinical guidelines. It can be assumed that within the framework of cancer prevention measures in the first years of follow-up of a patient with IBD from the onset of the disease, it is advisable to give priority to the risk of developing not only IBD-associated dysplasia, but also sporadic dysplasia of the colon mucosa.