- Objectives To evaluate comparatively fluorescence in situ hybridization (FISH) and cytology performed on exfoliated urothelial cells obtained from voided urine and bladder washings as a method of diagnosis and follow-up in patients with transitional cell carcinoma (TCC) of the bladder. Methods Thirty patients with confirmed bladder TCC, 10 patients enrolled in cystoscopy follow-up for previous bladder tumors, and 10 patients with bladders free of tumor without a previous history of bladder TCC underwent cytologic examination and FISH performed on voided urine and bladder washing specimens. The FISH probes were targeted to chromosomes 7 and 9. Results FISH had a sensitivity of 92% for high-grade tumors in both voided urine and bladder washing specimens, significantly greater than that of cytology at a sensitivity of 64% in voided urine and 67% in the bladder washing specimens (P = 0.02). The sensitivity of FISH and cytology were both low and not significantly different statistically from each other for the low-grade tumors. Monosomy of chromosome 9 correlated with early tumor recurrence. Polysomy of chromosomes 7 and 9 correlated with high-grade tumors (80% and 92%, respectively). Conclusions According to our results, with the local cytopathology expertise, FISH performed on urothelial cells from voided urine has a sensitivity that supersedes that of cytology, making the former a valuable complementary method in the diagnosis and follow-up of patients with bladder TCC.