Incidence of prostate cancer in Japan and resultant mortality rates are lower than in Western countries. To elucidate the reasons behind this, the genetic characteristics of prostate cancer in Japanese patients were investigated. Comparative genomic hybridization was applied in 27 cases of prostate cancers in Japanese patients. Frequent gains were found at Xq, 8q, Xp, and 7q and frequent losses at 8p, 6q, 2q, 16q, and 17p (in decreasing order of frequency). Loss of 6q was frequently detected in both early and advanced tumors. Gains of 7q and 8q and loss of 8p were more frequent in advanced than early tumors. The frequency of 13q loss in primary tumors was significantly lower in patients in Japan than in European countries. These data suggest that a loss of 6q is associated with the development of prostate cancer, and that gains of 7q and 8q and a loss of 8p are linked with cancer progression. The frequency of 13q loss may imply differences in biological behavior of prostate cancer between Japan and Western countries.