This study evaluated 28 patients to characterize the morphologic features associated with typical Crohn disease (CD). All patients had similar complaints, an endoscopically normal colon, and small isolated, aphthoid erosions in the terminal ileum. The mean length of follow-up was 5.8 years. Of 28 patients, 25 (89%) were female (mean age, 32.3 years). Four patients were ingesting nonsteroidal anti-inflammatory drugs. All 28 lesions were morphologically similar, with focal lamina propria edema, mild active inflammation, and crypt disarray. Most had a lymphoid aggregate within the region of edema. Erosion was identified histologically in 21 cases. Following colonoscopy, symptoms resolved in all 28 patients. Typical, full-blown CD developed in 8 patients (29%) after a mean interval of 3.6 years. CD lesions were morphologically identical to non-CD lesions. Most focal ileal erosions in patients with mildly altered bowel habits are idiopathic and clinically insignificant. They represent early CD in approximately 30% of patients. The interval between initial examination and typical CD can be long. Pathologists should remain diagnostically vigilant when examining ileal biopsy specimens obtained from patients with previous abnormal ileal biopsy findings, regardless of the interval. Persistent, mild morphologic abnormalities have a high likelihood of being CD.