About 10% of patients with colitis due to inflammatory bowel disease have indeterminate colitis. Despite newer diagnostic tools, the frequency has not diminished over the past 33 years. The current preferred term among academicians is colonic inflammatory bowel disease unclassified(IBDU), although indeterminate colitis is the term endorsed for inclusion in the ICD-10 coding system. Indeterminate colitis is more frequent among children. Theanti-Saccharomyces cerevisiae (ASCA) and perinuclear anti-cytoplasmic antibody (pANCA) are useful in distinguishing IBDU from ulcerative colitis and Crohn’s disease. However, current serologic and genetic studies, as well as endoscopic and imaging studies lack sufficient positive predictive values to make a definite diagnosis of Crohn’s colitis or ulcerative colitis. Patients with IBDU who undergo proctocolectomy with ileal pouch-anal anastomosis have more complications than patients with ulcerative colitis. Although some patients with indeterminate colitis eventually develop characteristic ulcerative colitis or Crohn’s disease, a subgroup are durably indeterminate.