One hundred forty-six consecutive specimens of excised bowel from patients with Crohn's disease were studied to determine the relationships between strictures, sinuses, and "fissures." A significant coincidence of sinuses and strictures was observed and sinuses tended to arise proximal to the point of maximal stricture. "Fissures," defined as blind-ending inflammatory tracts that did not penetrate through the full thickness of the muscle coat, were of two types. One type was associated with submucosal fibromuscular hyperplasia and repair and appeared to be an early sinus. The second type was in dilated ileum or colon in the bases of ulcers and is designated an "acute fissure." The anatomic findings suggest that both sinuses and fissures may be due to mechanical factors including intraluminal pressure rather than to any intrinsic quality of the inflammatory process in Crohn's disease.