The etiology of bladder cancer is well investigated. Bladder carcinogenicity of nitrosamines is proven in animals but not in men, although dimethylnitrosamine in urine of patients with urinary infections or bilharziosis suggest a causative role. Aromatic amines are strong bladder carcinogens. Arsen is proven to be bladder carcinogenic as well as the nitrofurane FANFT. Nitrofurantoin however is not bladder carcinogenic nor are the endogenous metabolites of tryptophan. The influence of papilloma virus on bladder carcinoma induction ist not definitely proven yet. Bilharziosis or chronic urinary infections correlate with bladder carcinomas, nitrosamines being the possible reason. The reason for the increased incidence of bladder carcinomas in balkan nephropathy ist not clear. Arcolein as a metabolite of Cyclophosphamid is a strong bladder carcinogen as well as Phenacetin. Immune suppression and radiotherapy are risk factors, too. About 50% of bladder carcinomas are due to cigaret smoking.