Table 1

 Vienna and Montreal classification for Crohn’s disease

*L4 is a modifier that can be added to L1–L3 when concomitant upper gastrointestinal disease is present.
†“p” is added to B1–B3 when concomitant perianal disease is present.
Age at diagnosisA1 below 40 yA1 below 16 y
A2 above 40 yA2 between 17 and 40 y
A3 above 40 y
LocationL1 ilealL1 ileal
L2 colonicL2 colonic
L3 ileocolonicL3 ileocolonic
L4 upperL4 isolated upper disease*
BehaviourB1 non-stricturing, non-penetratingB1 non-stricturing, non-penetrating
B2 stricturingB2 stricturing
B3 penetratingB3 penetrating
p perianal disease modifier†