In vivo endoscopic optical coherence tomography (OCT) was performed in 154 patients with pathologic lesions, suspicious for high-grade dysplasia, intramucosal or early microinvasive cancer. One group of seven physicians and another of six, familiar with OCT, participated in the blinded recognition of benign and neoplastic conditions in different types of mucous membranes. The result for the OCT sensitivity for malignancy detection in these types of mucosa is 83 - 98%, specificity 71 - 91%. The accuracy was 81 - 87%. Recognition error rate is smaller for high-grade dysplasia and invasive cancer in urinary bladder (3.3% - 1.5%), and higher for the uterine cervix (23% - 11%) and for larynx (45.7% - 3.4%). The kappa coefficient for interobserver agreement was 0.65-0.83.