Ileitis, or inflammation of the ileum, is often caused by Crohn's disease. However, ileitis may be caused by a wide variety of other diseases. These include infectious diseases, spondyloarthropathies, vasculitides, ischemia, neoplasms, medication-induced, eosinophilic enteritis, and others. The clinical presentation of ileitis may vary from an acute and self-limited form of right lower quadrant pain and/or diarrhea, as in the majority of cases of bacterial ileitis, but some conditions (ie, vasculitis or Mycobacterium tuberculosis) follow a chronic and debilitating course complicated by obstructive symptoms, hemorrhage, and/or extraintestinal manifestations. Ileitis associated with spondylarthropathy or nonsteroidal anti-inflammatory drugs is typically subclinical and often escapes detection unless further testing is warranted by symptoms. In a minority of patients with long-standing Crohn's ileitis, the recrudescence of symptoms may represent a neoplasm involving the ileum. Distinguishing between the various forms of ileitis remains a test of clinical acumen. The diagnosis of the specific etiology is suggested by a detailed history and physical examination, laboratory testing, and ileocolonoscopy and/or radiologic data.