While a general appreciation for the importance of chromosomes in the development of cancer has existed for decades, molecular genetic analyses have gained considerable attention in recent years through identification of proto-oncogenes and tumor suppressor genes. Several different chromosomal aberrations, alterations of proto-oncogenes and suppressor genes have been described in prostate cancer. Loss of genetic material has been found to occur most frequently on chromosomes 7, 8, 10 and 16. The existence of tumor suppressor genes relevant to prostate carcinogenesis is suspected in these chromosomal locations. Several investigators are currently trying to identify these genes. Altered expression of several different oncogenes has been reported in prostate cancer. Among these, the ras- and myc-families of oncogenes have been studied most intensively. Structural oncogene alterations have been detected infrequently, most of the changes appear to occur transcriptionally. Despite an abundance of clinical material, knowledge about genetic lesions in prostate cancer is still very limited and sometimes conflicting results have been reported. With recent methodologic improvements and a growing interest in correlating genetic alterations with clinical disease progression, definition of prostate carcinogenesis at the molecular level will advance rapidly in the near future.