Objective: Previous studies on touch biopsy specimens have determined numerical or structural changes involving many different chromosomes in bladder cancer. The aim of this study was to evaluate the use of fluorescence in situ hybridization (FISH) assay in bladder washings as an objective technique to detect chromosomal numerical aberrations in bladder cancer. The main advantages of bladder washings are that they can be easily collected during the clinical follow–up of patients with superficial bladder cancer and they do not contain so many degenerate cells as urine samples. Methods: We collected specimens from 25 patients who underwent transurethral resection of bladder tumors. Double target FISH assays with centromeric labeled probes for chromosomes 7, 8, 9 and 11 were used on the bladder washings and on the touch biopsy slides. The results were compared to flow cytometry and tumor grade and stage. Results: We found monosomy 9 and trisomy 7, 8, 9 and 11 in 28, 32, 36, 28 and 25% respectively of the patients. FISH analysis of bladder washing versus touch biopsy specimens were concordant in approximately 90% of the slides. Total DNA aneuploidy correlated well with numerical aberrations of chromosomes 7, 8 and 11, but not with chromosome 9. Conclusion: Although better hybridization efficiency was obtained on touch biopsy slides, the results in bladder washings were in high concordance. FISH analysis on bladder washing samples may become a simple tool to improve the accuracy of cytology.