Which inflammatory bowel disease often leads to complications like strictures and fistulas?

Crohn's disease is the correct choice because it is known for causing complications such as strictures and fistulas due to its ability to affect any part of the gastrointestinal tract from the mouth to the anus and its tendency to involve the full thickness of the bowel wall. This transmurally penetrating nature leads to the development of inflammation and lesions that can create strictures, which are narrowing of the intestines, and fistulas, which are abnormal connections that may form between different parts of the bowel or between the bowel and other organs.

In contrast, ulcerative colitis typically only affects the colon and rectum and primarily involves the mucosal layer of the bowel wall. While it can lead to complications, such as toxic megacolon or colorectal cancer, strictures and fistulas are less common in ulcerative colitis compared to Crohn's disease.

Irritable bowel syndrome (IBS) is primarily a functional disorder and does not cause inflammation, strictures, or fistulas, making it irrelevant in this context. Therefore, Crohn's disease is the primary condition associated with these specific complications.