Abstract. Bladder cancer is a common malignancy. Recurrence rate and progression vary greatly depending on factors such as tumor multiplicity, size, previous recurrence rates, tumor stage, tumor grade and the presence of carcinoma in situ. Treatment is expensive, recent studies demonstrated that superficial bladder cancer is a major economic burden. It is necessary to establish new kinds of techniques to improve diagnosis, therapy and follow-up, such as fluorescence diagnosis, without adding significant risk of complications. As urologists have a better sight of bladder lesions with fluorescence diagnosis, pathologists will be asked in the future to evaluate more frequently flat lesions, which up to now would not have been a matter of concern. For several reasons it is very important to have accurate and precise definitions of these flat lesions. First to permit uniform treatment of large groups of patients and second to see in large cohorts the evolution and natural history of several flat lesions, not always well known up to now. The aim of the study was to review the most important flat lesions, to demonstrate the difficulty of classifying several lesions, to introduce to urologists the new problems linked to FD and to suggest new models for accurate analysis. How far can we go in our answer as pathologists and how will it change the patient management?