Ulcerative colitis and Crohn's disease are the most common forms of inflammatory bowel disease (IBD). Some people have a nonspecific form of IBD that is like ulcerative colitis but doesn't have all its features. This may be a different type of ulcerative colitis.

For up to 10% of people who have symptoms, neither Crohn's disease nor ulcerative colitis can be diagnosed.¹ These people have a form of IBD called indeterminate colitis, which doctors believe is a combination of Crohn's disease and ulcerative colitis.