Direct autofluorescence endoscopy of the larynx has proven to facilitate the detection and delineation of precancerous lesions, carcinoma in situ and cancer. The aim of the present study was to evaluate the diagnostic potential and limitations of this imaging technique applied during indirect laryngoscopy. In a prospective study, 116 patients with suspected precancerous or cancerous lesions were investigated preoperatively by indirect autofluorescence laryngoscopy. Autofluorescence was induced by filtered blue light (375-440 nm) of a xenon short-arc lamp and processed by a CCD camera system (D-light-AF System, Storz, Tuttlingen, Germany). Autofluorescence images were immediately assessed for diagnosis, compared to the direct autofluorescence picture obtained during microlaryngoscopy and compared to pathohistological findings. Comparable to direct autofluorescence images, normal laryngeal mucosa showed a typical green fluorescence signal. Moderate and high epithelial dysplasia, carcinoma in situ and cancer displayed a diminished green fluorescence. False negative results were related to extreme hyperkeratosis. False positive cases showed mild dysplasia with inflammatory reactions or scarring. In 103 cases (89%), we found concordant results. According to our results, the presented technique seems to be a promising diagnostic tool for the early detection of laryngeal cancer and its precursor lesions during indirect laryngoscopy. Scarring, marked hyperkeratosis and inflammation can limit the predictive value of the method.