Bladder cancer progression is thought to be associated with sequential genetic events. To search for the specific genetic changes associated with the metastatic process, comparative genomic hybridization was performed on 22 primary tumors and 24 metastases (10 distant and 14 nodal metastases) from 17 patients with stage pT2-4 bladder cancer. There was a striking similarity between the genetic alterations present in the primary and metastatic tumor samples from the same patient. The mean number of genetic changes/tumor was 12.2 for primary tumors and 11.7 for metastases. There was a strong concordance in the specific aberrations present in each patient's primary and metastatic lesions (mean, 75%). Concordance was also high among multiple sites from an individual primary tumor (mean, 96%) and multiple metastases from the same patient (mean, 75%). There were no specific genetic changes overrepresented in the metastases compared with their primary tumors. Genetic alterations present in more than 40% of tumors included gains on 6p, 8q, 10q, and 17q and losses involving 8p, 10q, and Y. Two regions of high-level amplification were common: (a) 10q22.1-q23.1 (32.6%); and (b) 17q11-21.3 (23.9%; the locus of erbB-2). A summary statistic was developed to quantitate the degree of clonal relationships between biopsies from the same patient. These data support a model in which minimal clonal evolution occurs in the metastatic tumor cell population after the metastatic event. When comparing primary cancers from patients with and without metastases, however, several unique genetic changes were identified in those cancers with metastases, suggesting that these loci may harbor genes important to the metastatic process.