The recently introduced fluorescence in situ hybridization method (FISH method) is a chromosomal analysis for examining interphase nuclei and seems to be a promising approach for chromosomal analysis of a solid tumor, which is considered hard to deal with by a conventional chromosomal staining method. In the present study, a bladder tumor (transitional cell carcinoma) was evaluated by chromosomal analysis, including interphase nuclei, with this FISH method to examine chromosomal numerical aberration in relation to the grade and stage, expecting successful, accurate determination of reliable prognostic factors based on its relapse and invasive intensity. Tissue specimens obtained from 20 patients with bladder tumor (transitional cell carcinoma) were used. The probe used in this study was specific for chromosome No. 1, 7, and 9, which were frequently indicated as being abnormal by a conventional chromosomal staining method. As a result, a tendency towards polysomy was observed in chromosome No. 1 and 7 of high grade invasive cancer cases, while a tendency towards monosomy was evident in chromosome No. 9 of low grade noninvasive cancer cases. From the results mentioned above and consideration of related literatures, it was suggested that monosomy of chromosome No. 9 is important as an index for knowing changes in the initial developmental stage of bladder tumor and polysomy of chromosome No. 1 and 7 is important as an index for knowing changes in the progressive stage.