The two main types of inflammatory bowel disease (IBD) are Crohn's disease and ulcerative colitis. Currently, when IBD is suspected, CT enterography is widely used as an initial imaging test because it can evaluate both the bowel wall and the outside of the bowel, helping to differentiate IBD from other diseases. When IBD is suspected, it is necessary to distinguish between Crohn's disease and ulcerative colitis. In most cases this is not difficult; however, in some cases, it is difficult and such cases are called IBD-unclassified. CT findings are often non-specific for ulcerative colitis, making it difficult to differentiate it from other diseases using imaging alone. In contrast, characteristic CT findings for Crohn's disease are often helpful in diagnosis, although diseases, such as tuberculous enteritis can mimic Crohn's disease. Recently, mutations in the gene encoding a prostaglandin transporter called SLCO2A1 have been discovered as the cause of the disease in some patients with multiple ulcers and strictures, similar to Crohn's disease. Therefore, genetic testing is being used to make a differential diagnosis.