In Europe, cancer of the bladder is the fourth most common cancer among men, accounting for 7% of total cancers. In the USA, bladder cancer is the fifth most common cancer in men and seventh in women. This disease is three times more common in men than in women. Several risk factors, such as cigarette smoking and occupational chemical exposure, contribute to bladder cancer development. The balance between activation and detoxification of carcinogens affects the amount of DNA damage that accumulates in cells. The entire process leading to DNA damage and subsequent repair of the damage involves a host of enzymes, many of which are polymorphic. Polymorphisms in metabolic enzyme genes and repair genes may cause alterations in protein product functions that can finally lead to genomic instability and carcinogenesis. In this article, we review the polymorphisms in a number of genes that have been found to be the modulators of bladder cancer risk. Improved understanding of the molecular biology of urothelial malignancies is helping to more clearly define the role of new prognostic indices and multidisciplinary treatment for this disease.