BACKGROUND AND AIMS: Peyer's patches play a major role in intestinal immunity, 
are portals of entry for significant pathogens, and may be important in Crohn's 
disease. Whereas their microscopic anatomy and immune function are well 
described, surprisingly little is known of their macroscopic anatomy and 
distribution. Our aim was to assess their number, area, and distribution in the 
normal distal ileum, with particular reference to patient age.
METHODS: Distal ilea (200 cm) obtained at autopsy from 55 adults without 
intestinal disease were opened along the mesenteric border, fixed in acetic 
acid, and transilluminated. Peyer's patches were counted, and the length, 
breadth, and distance from the ileocecal valve were recorded.
RESULTS: Patches were most numerous in the terminal 10-15 cm where they formed a 
lymphoid ring. More proximal patches were oval, antimesenteric, and irregularly 
spaced. By area, 46% of patch tissue occurred in the terminal 25 cm. The mean 
number of patches ranged from 29.4 +/- 5.4 in the youngest group studied, to 
19.0 +/- 3.0 in the oldest. Total patch area was greatest in the group aged 
21-30 (47.4 +/- 1.0 cm2).
CONCLUSION: Peyer's patches are concentrated in the distal 25 cm of ileum but 
extend proximally for 200 cm. The variation in their size, shape, and 
distribution in different individuals is greater than often appreciated and may 
influence the presentation of diseases centered on these structures.