Table 1.

Montreal classification

Classification	Description
Age of onset (A)
A1	16 years old or younger
A2	17-40 years old
A3	Over 40 years old
Location (L)
L1	Terminal ileum
L2	Colon
L3	Ileocolon
L4	Upper gastrointestinal
Behavior (B)
B1	Non-stricturing, non-penetrating
B2	Stricturing
B3	Penetrating