Age at diagnosis
A1 ≤ 16 years
A2 17 ~ 40 years
A2 > 40 years
L1 Terminal ileum (the lower third of the small bowel with or without spill over into cecum)
L2 Colon
L3 Ileocolon (terminal ileum + any location between ascending colon and rectum)
L4 Isolated upper disease (a modifier that can be added to L1-L3 when concomitant upper gastrointestinal disease is present)
B1 Nonstricturing nonpenetrating
B2 Stricturing
B3 Penetrating
p perianal disease modifier (added to B1-B3 when concomitant perianal disease is present)