The bladder constitutes the most frequent localization of malignant tumors in the urinary tract. Further prognostic factors are molecular and cytogenetic alterations, which have been identified as key mechanisms in the carcinogenetic pathway of bladder cancer. Structural or numerical chromosomal alterations lead to the activation of a variety of cancer-inducing oncogenes as well as to the inactivation of various distinct antiproliferative tumor-suppressor genes. With regard to the biological heterogeneity in transitional cell carcinoma, which is also reflected in epidemiological data, the differing clinical course and the limited value of established prognosticators, the analysis of new molecular parameters has become of interest in predicting the prognosis of bladder cancer patients. In addition, the definition of high-risk patient groups that are at at risk of progression and recurrence is a further objective of urological research in this field.