Flow cytometry (FCM) of bladder cancer has unique characteristics. First, bladder washing is a suitable material to measure in terms of single cell suspension, while the urine appears inadequate because of the low sensitivity for detecting bladder cancer. Second, the role of FCM depends on the different features of superficial, in situ or invasive bladder cancer. In superficial cancers, FCM can detect the presence of cancer, predict intravesical recurrence and evaluate the response of intravesical instillation therapy. In carcinomas in situ, frequent occurrence of polyclonal aneuploid may indicate the aggressive nature of high grade malignancy. Early removal of bladder may be endorsed unless BCG instillation is effective. For invasive cancers, FCM does not seem to be so useful, but FCM relates well to other prognostic parameters.