Objective To evaluate the clinical application value of dual color fluorescence in-situ hybridization (FISH) in detecting urothelial carcinoma of the urinary bladder.MethodsThe probes of chromosome 3,7,17centromeres and chromosome 9p21 region (p16) were labeled by random primer method.FISH was performed on interphase nuclei of 80 urine specimens of cancer of the urinary bladder and 20 cases of healthy persons served as normal controls.Threshold value was established.The pathological diagnosis was the golden standard.Chromosome aberration was counted.The correlations between chromosome aberration and pathologic grading and staging and their sensibility of diagnosis for urothelial carcinoma of the urinary bladder were analyzed. Results The rate of numerical aberration of chromosome 3,7,17,9p21 was 47.5％(38/80),60.7％ (49/80),51.3％ (41/80) and 58.8％ (47/80) respectively.The positive rate of the combined use of 3,7,17 and 9p21 chromosome probes for detecting urothelial carcinoma of urinary bladder was 76.3％ (61/80).The aberrations had no correlation to tumor stage.The aberration of chromosome 3,7 and 17 were correlated to pathologic grade significantly (P ＜ 0.05).ConclusionThe progression of urothelial carcinoma of the urinary bladder is related to the aberrations of chromosome.FISH is believed to be a very important method in diagnosis of urothelial carcinoma of the urinary bladder,which may have important clinical significance for the postoperative recurrence detection and prognosis.