To evaluate the practical usefulness of flow cytometry (FC) applied to bladder wash specimens for the diagnosis of transitional cell carcinoma (TCC), a study was conducted on a series of 101 cases comprising 60 patients with tumor or with past history of TCC, and a control group of 41 patients undergoing cystoscopy for causes other than TCC in which the absence of tumor was confirmed after 1 year of follow-up. When results of the 33 patients with tumor were compared with those of the control group, FC gave low specificity and positive predictive values (54% and 58%, respectively). Conventional cytologic study was superior to FC in this setting. Although the combination of both techniques increased the sensitivity for low-grade tumors, specificity remained lower than that of cytologic study alone. Otherwise, when considering only the cases with a past history of TCC, results of FC were superior to those of cytologic examination, and the combination of both techniques gave high sensitivity and negative predictive values (94% and 93%, respectively). In conclusion, the use of FC in a general diagnostic setting could be misleading, whereas in the follow-up of patients with a history of TCC it becomes a useful adjunct to cytologic study in order to obtain a high diagnostic performance that could allow cystoscopies to be spaced out in these patients.