The understanding of the cell cycle and the control of cellular proliferation has increased dramatically over the past years. Cancer is most likely caused by multiple genetic aberrations, therefore it seems likely that one or more genes involved in tumorigenesis will regulate a portion of the cell cycle. Cell cycle related genes, such as p53 are becoming important in determining prognosis. In addition, gene replacement therapy for a deleted gene may hold promise in treating malignancies. Further understanding of cell proliferation should bring marked improvements in the diagnosis and treatment of genitourinary malignancies.