The authors report the results of a 5-year experience with flow cytometry (FCM) in the diagnosis and evaluation of bladder tumors. FCM was applied to 400 patients (225 without a urinary tumor and 175 with a past or recent bladder tumor). For the patients without a tumor, bladder-irrigation-fluid FCM was positive in 22% of samples vs 1% of those tested with conventional cytology. The high rate of false-positive results may have been due to an imperfect quality of the samples, to the staining procedure and to the high amount of squamous cells. For 72 selected tumors in which the bladder washing was performed under specific requirements, the detection rate of FCM was lower than that of conventional cytology, including G1-grade tumors. A comparison between bladder-irrigation-fluid FCM and disaggregated-biopsy FCM revealed a 22% rate of discordant results. From these data it does not seem desirable tu use bladder-irrigation FCM instead of conventional cytology in routine urologic examinations. The use of this technique must be more selective in bladder tumor evaluation.