Prostate cancer is the most commonly diagnosed male malignancy in western countries. Recent work in cell biology and molecular cytogenetics has led to a large amount of data on chromosomal abnormalities in prostatic tumors. A highlight of the literature describing both classical and molecular cytogenetic studies of prostate cancer is presented. By conventional cytogenetics, predominant changes included gain of chromosome 7, loss of Y, deletions of 7q and 10q, and the appearance of double minutes. Using fluorescence in situ hybridization, predominant changes included gains of chromosomes 1, 7, 8, 8q sequences, 17, X and Y, and loss of chromosomes 1, 7, 8, 8p sequences, 10, 10q, 16q and 17q sequences, 17 and Y. Newly defined sites by comparative genomic hybridization included loss of genetic material on 2q, 5q, 6q, 9q, 13q, 15q, 17p, and 18q, and gains at 1q, 2p, 3q, 7q, 9q, 11p, 16p, 20, 22, and X. These data indicate that multiple non-random genomic sites are involved in prostate tumorigenesis. This wide and relatively recent gain of information is likely to provide key clues to the biologic basis of this disease.