We describe the design and performance tested during six years of clinical trials of a fluorescence endoscope for the detection and delineation of cancers in several hollow organs. The apparatus is based on the imaging of the laser-induced fluorescence that differs between a tumor and its surrounding normal tissue. The tests are carried out in the upper aerodigestive tract, the tracheobronchial tree, the esophagus, and the colon. In the three former cases an exogenous dye is used (Photofrin II), whereas in the latter case fluorescein molecules conjugated with monoclonal antibodies directed against carcinoembryonic antigen are injected. The decrease of native tissue autofluorescence observed in early cancers is also used for detecting lesions in the tracheobronchial tree. The fluorescence contrast between the tumor and surrounding normal tissue is enhanced by real time image processing. This is done by simultaneously recording the fluorescenceimage in two spectral domains, after which these two images are digitized and manipulated with a mathematical operator (look-up table) at video frequency. Moreover, the device that is described below allows for an immediate observation of the endoscopic area under white light illumination during fluorescence detection in order to localize the origin of the “positive” fluorescence signals. Typical results obtained in the tracheobronchial tree and in the colon are presented and the sources of false positives and false negatives are evaluated in terms of the fluorescent dye, tissue optical properties, and illumination optics.