Purpose: Optical coherence tomography (OCT) is an optical imaging method that can visualize cellular and extracellular structures at and below tissue surface. The objective of the study was to determine if OCT could characterize preneoplastic changes in the bronchial epithelium identified by autofluorescence bronchoscopy. Experimental Design: A 1.5-mm fiberoptic probe was inserted via a bronchoscope into the airways of 138 volunteer heavy smokers participating in a chemoprevention trial and 10 patients with lung cancer to evaluate areas that were found to be normal or abnormal on autofluorescence bronchoscopy. Radial scanning of the airways was done to generate OCT images in real time. Following OCT imaging, the same sites were biopsied for pathologic correlation. Results: A total of 281OCT images and the corresponding bronchial biopsies were obtained.The histopathology of these areas includes 145 normal/hyperplasia, 61metaplasia, 39 mild dysplasia, 10 moderate dysplasia, 6 severe dysplasia, 7 carcinoma in situ, and 13 invasive carcinomas. Quantitative measurement of the epithelial thickness showed that invasive carcinoma was significantly different than carcinoma in situ (P = 0.004) and dysplasia was significantly different than metaplasia or hyperplasia (P = 0.002). In addition, nuclei of the cells corresponding to histologic results became more discernible in lesions that were moderate dysplasia or worse compared with lower-grade lesions. Conclusion: Preliminary data suggest that autofluorescence bronchoscopy^guided OCT imaging of bronchial lesions is technically feasible. OCT may be a promising nonbiopsy tool for in vivo imaging of preneoplastic bronchial lesions to study their natural history and the effect of chemopreventive intervention.Lung cancer is the most common cause of cancer death worldwide, with more than 1.3 million people dying of lung cancer annually (1). The 5-year survival rates after the diagnosis of lung cancer has improved only marginally in the last 3 decades (2). Although early detection and chemoprevention is effective in reducing the incidence and mortality of cancer of the breast, there is considerable skepticism in applying the same cancer control strategy in lung cancer. The most common criticism is the uncertain identity of intraepithelial neoplastic (IEN) lesions and the natural history of these lesions.There are unique challenges in detecting and treating IEN lesions in the lung compared with other organs. The lung is an internal organ consisting of a complex branching system of conducting airways leading to gas exchange units. Lung cancer consists of four major cell types: squamous cell carcinoma, adenocarcinoma, large cell carcinoma, and neuroendocrine tumors (3). They are preferentially located in different parts of the bronchial tree. For example, squamous cell carcinoma and neuroendocrine tumors are more frequently found in the larger central airways compared with adenocarcinoma, which is more frequently found in the small peripheral airways and lung parenchyma. Au...