Nowadays, bladder cancer is the fourth most common cancer in adults and the second most frequent urogenital tumor. Predicting recurrence and progression of superficial bladder tumors, with available clinical information to decide the therapy to be used is a difficult task. In this work, two mathematical models were developed to help specialists on the decision process. The mathematical tool used to formulate the model was the fuzzy sets theory, due to its capacity in dealing with uncertainties inherent in medical concepts. In the first model, Stage, Grade and Size of the tumor were also considered input variables and Risk of Recurrence of a superficial bladder tumor as output variable of the first Fuzzy Rule-Based Systems (FRBS). In the second model, in addition to the Stage, Grade and Size of the tumor, it was also considered as input variable of a second FRBS Carcinoma in situ and, the Risk of Progression of superficial tumors as an output variable. For each model, simulations were made with data originated from of patients of the Clinics Hospital/ UNICAMP and A. C. Camargo Hospital of São Paulo, with the aim to verify the reliability of results generated by the two systems. From a database and the possibility found by FRBS, after the possibility-probability transformation, we can generate the real probability of each fuzzy output set.