Early diagnosis and treatment of malignant tumors of the mouth and throat can greatly improve survival rates. Diagnostic fluorescence permits the reliable detection not only of oral cancer, but also of cancer precursor lesions. A problem here is the fact that although carcinomas can be detected with a high level of sensitivity, our own studies also demonstrate a considerable false-positive rate (35%). Possible reasons for this currently being considered are non-compliance by the patient with the required fasting period, poor mouth hygiene and the state after radiation therapy to the face. Under these circumstances, patient management is of particular importance.