A 60-year-old male with ileocolic Crohn's disease diagnosed 36 years earlier (Montreal Classification: A2, L3, B1) underwent a surveillance colonoscopy. The examination revealed an 11 mm flat lesion in the transverse colon, presenting as a reddish plaque with indistinct borders under white light. Narrow band imaging (NBI) showed a regular vascular pattern and crypt distribution. Endocytoscopy, after staining with crystal violet and methylene blue, revealed elongated crypts and uniform fusiform nuclei, consistent with a tubular adenoma. En bloc resection was performed using underwater mucosal resection. Histology confirmed a tubular adenoma with low-grade dysplasia and clear resection margins.