|Aims:Chromoendoscopy, narrow-band imaging (NBI), and confocal laser endomicroscopy (CLE) have been introduced in ulcerative colitis-associated neoplasia (UCAN) surveillance. We aimed to determine the morphological features of UC-associated colorectal cancer (UCAC) at magnifying narrow band imaging (M-NBI) and magnifying chromoendoscopy with crystal violet, and the ability of CLE to differentiate among UCAC (differentiated type or undifferentiated type), sporadic adenoma, and circumscribed regenerative lesions. Methods:For morphological analysis, 31 UCAC of 28 patients and 14 UC-associated dysplasia of 12 patients were enrolled. For CLE analysis, 12 lesions of 12 consecutive patients with suspected or established UCAN were enrolled. We performed probe-based CLE (pCLE) on 12 patients in addition to M-NBI and magnifying chromoendoscopy. We compared pCLE findings with pathologic diagnoses.Results:UCAC and dysplasia had a variety of morphological types, but the pit patterns VI or VN tended to correspond to malignant pathology. pCLE could differentiate UCAC from other pathologies such as solitary adenoma and non-neoplastic circumscribed regenerative lesions on the basis of back-to-back orientation of crypts (P=.048), and UC-associated undifferentiated cancer from other pathologies on the basis of dark trabecular architecture (P=.015). Sensitivity, specificity, and accuracy of combination of back-to-back orientation of crypts and dark trabecular architecture for carcinoma or dysplasia was 100%, 83%, and 92%, respectively. Conclusions:In vivo microscopic observation with pCLE was helpful to evaluate the suspected UCAN.