Table 3.

Montreal Classification for CD^a

Clinical Factors	Classification
Age at diagnosis	A1: ≤ 16 years A2: 17 to 40 years A3: > 40 years
Disease location	L1: ileal L2: colonic L3: ileocolonic L4: upper GI tract*
Disease behavior	B1: Nonstricturing, nonpenetrating B2: stricturing B3: penetrating P: perianal disease**

Notes: ^aData from Silverberg MS, Satsangi J, Ahmad T, et al. Toward an integrated clinical, molecular and serological classification of inflammatory bowel disease: report of a Working Party of the 2005 Montreal World Congress of Gastroenterology. Can J Gastroenterol. 2005;19 Suppl A:5A-36A.45 ≤, Less than or equal to; >, greater than; *L4 is a modifier that can be added to L1-L3 when concomitant upper GI disease is present. **P is added to B1-B3 when concomitant perianal disease is present.