Résumé : Cutaneous Fluorescence Diagnosis (FD) is a new promising dermatological procedure which is based on the combination of a local application of a photosensitizer such as 5-aminolevulinic acid (ALA) or its methyl ester (MAL) and the use of a light source (red light) adapted to the absorption spectrum of these molecules. The targeted photosensitization of skin cancers, particularily superficial and extensive lesions including superficial basal cell carcinoma and Bowen's disease, by ALA or MAL induced porphyrins leads to a selective red fluorescence which can be demonstrated by Wood's lamp. This technique may be useful either to define better the choice of margins or to detect earlier and or multifocal recurrences.