A retrospective study was carried out on 200 consecutive superficial transitional cell carcinomas of the bladder in order to identify which factors could influence the recurrence and/or progression of the tumor. Many parameters were considered, such as stage, grade, number, size, site, tumor-free interval and bladder mucosa mapping. A careful histological study of the initial tumor was employed and the tumors confined to the stromal core of the papillary tumor (T1a) were separated from those with invasion of the lamina propria of the bladder wall (T1b). The behavior of the T1b lesions observed in our study will be discussed in a forthcoming article. Recurrence occurred in 83% of our patients, and it was influenced by number and grade of the tumor and by the presence of dysplasia in normal-appearing mucosa. In 20% of our patients tumor progression occurred. Tumor progression was correlated with invasion of the lamina propria of the bladder wall, high-grade neoplasias, tumor-free interval, dysplasia or carcinoma in situ in normal-appearing mucosa. The results of our study suggest that, by these risk factors, a better prediction of the behavior of superficial transitional cell carcinoma and, as a consequence, more appropriate treatment can be provided.