Development and progression of tumors is driven by a malfunction of specific genes. Although prostate cancer is one of the most frequent tumors, little is known about the genes involved. Cytogenetic and molecular examinations have shown that chromosomal deletions most frequently involve 7q, 8p, 10q, 13q, 16q, 17p and the Y chromosome. These loci may carry tumor suppressor genes with relevance for prostate cancer. DNA sequence copy number gains were most frequently observed at chromosomes 7, 8q, and 11q. These regions may carry currently unknown oncogenes. There is increasing evidence for a clinical relevance of genetic alterations. Polysomies of several chromosomes were shown to be associated with poor prognosis of prostate cancer patients. Androgen receptor amplification can be found in hormone-refractory carcinomas which may respond to total androgen blockage. For the future it is hoped that the identification of the genes involved in prostate cancer and the determination of their function could allow for significant improvements of treatment strategies for prostate cancer patients.