AIM: To identify pathologic features associated with this "ulcerative colitis (UC)-like" subgroup of Crohn's disease (CD). METHODS: Seventeen subjects diagnosed as having UC who underwent proctocolectomy (RPC) from 2003-2007 and subsequently developed CD of the ileal pouch were identified. UC was diagnosed based on pre-operative clinical, endoscopic, and pathologic studies. Eighteen patients who underwent RPC for UC within the same time period without subsequently developing CD were randomly selected and used as controls. Pathology reports and histological slides were reviewed for a wide range of gross and microscopic pathological features, as well as extent of disease. The demographics, gross description and histopathology of the resection specimens were reviewed and compared between the two groups. RESULTS: Patients with "UC-like" CD were on average 13 years younger than those with "true" UC (P < 0.01). More severe disease in the proximal involved region and active ileitis with/without architectural distortion were observed in 6 of 17 (35%) and 7 of 17 (41%) "UC-like" CD cases, respectively, but in none of the "true" UC cases (P < 0.05). Active appendicitis occurred in 8 of 16 (50%) "UC-like" CD cases but in only two (11%) "true" UC cases (P < 0.05). Conspicuous lamina propria neutrophils were more specific for "UC-like" CD (76% vs 22%, P < 0.05). In addition, prominent lymphoid aggregates tended to be more common in "UC-like" CD (P = 0.07). The "true" UC group contained a greater number of cases with severe activity (78% vs 47%). Therefore, the features more commonly seen in "UC-like" CD were not due to a more severe disease process. Crohn's granulomas and transmural inflammation in non-ulcerated areas were absent in both groups. CONCLUSION: More severe disease in the proximal involved region, terminal ileum involvement, active appendicitis, and prominent lamina propria neutrophils may be morphological factors associated with "UC-like" CD.