The prognosis of superficial bladder cancer in terms of local recurrence and transformation into invasive cancer is related to the multiplicity of tumor sites and the concomitant presence of "flat" tumours, such as dysplasia and carcinoma in situ. This study of 51 patients emphasizes the value of fluorescence cystoscopy in the early detection of superficial transitional cell carcinomas. This method is based on induction of fluorescence in carcinomatous sites which selectively accumulate an endogenous photosensitizer, protoporphyrin IX, in response to intravesical administration of its precursor, 5-aminolevulinic acid. The sensitivity of the method in the present series was close to 93%. Fluorescence cystoscopy is a simple and reliable method to map the bladder mucosa looking for areas of dysplasia and carcinoma in situ.