Development of malignant tumors in patients with inflammatory bowel diseaseBackground: The chronic inflammation of the intestinal mucosa, the extra-intestinal manifestations of the disease and the immunosuppressive treatment of inflammatory bowel disease may increase cancer risk.Aim: To report the demographic and clinical features of patients with IBD who developed a malignant tumor.Material and Methods: Retrospective analysis of an IBD patient registry of a private clinic, diagnosed between 1976 and 2014.Results: 437 subjects were included, aged 15-88 years (58% women).Seventy two percent of patients had ulcerative colitis.The median time of follow up was 6 years.Ten patients (2.3%) developed a malignant tumor.In four, the tumor could be related to IBD (two colorectal cancers, one cholangiocarcinoma and one chronic myeloid leukemia (CML)).Two of 45 patients treated with biological therapy developed a tumor (CML and hypernephroma).Three of 170 patients on immunosuppressive treatment developed tumors.Only one had a tumor possibly related with the use of azathioprine (non-melanoma skin cancer).In only two patients, the treatment was changed at the time of their cancer diagnosis, from immunosuppressive medications to mesalamine.Conclusions: Only a small proportion of these patients with IBD developed a malignant tumor.The treatment of IBD has to be determined by the severity of the disease and not by the fear of developing a neoplasia.Following recommendations is fundamental to decrease the possibility of developing this complication.