Montreal Classification of Crohn's Disease Age at diagnosis (A1-A3): A1: < 16 yo A2: 16-40 yo A3: > 40 years Location (L1-L4): L1: ileal L2: colonic L3: ileocolonic L4: upper Gl Behavior (B1-B3 + p): B1: Inflammatory B2: Stricturing (inflamm, fibrostenotic) B3: Penetrating (fistula, abscess) p: Perianal #Montreal #Classification #Crohns #Disease #ibd #diagnosis #gastroenterology