The Lung Imaging Fluorescence Endoscope (LIFE) system has been developed to visualize preinvasive lesions in the tracheobronchial mucosa based on the difference of the auto fluorescence pattern between normal and neoplastic tissue. A prevalence study was performed in a group of patients known to be at risk for dysplasias and carcinomas in situ, using LIFE in combination with conventional fiberoptic bronchoscopy. These examinations were performed in a sequential but random manner. Thirty-three patients (29 men), with a mean age of 66 years (range. 43–82 years) were examined. All abnormal and suspicious lesions plus at least one specimen from a normal area were sampled separately. The respective results of LIFE and conventional bronchoscopy for detection of the combined moderate dysplasias, severe dysplasias, and carcinomas in situ were sensitivity, 89% (8 of 9) and 78% (7 of 9); specificity, 61% (77 of 126) and 88% (111 of 126); positive predictive values, 14% (8 of 57) and 32% (7 of 22); and negative predictive values. 99% (77 of 78) and 98% (111 of 113). LIFE is slightly more sensitive than the conventional bronchoscope in this select group of patients for the detection of preinvasive lesions at the cost of lower specificity and positive predictive value.