Introduction: Adenocarcinoma of the prostate is the most prevalent visceral malignancy in the male population and one of the leading causes of death of men. Despite such a high incidence, the prevalence of silent or latent cancers is shown to be much higher than the clinically diagnosed cases. Previous data on men undergoing radical cystoprostatectomy for muscle-invasive bladder cancer showed a 17-70% incidence of unsuspected prostate cancer which is higher than expected in general population. In addition to this, involvement of the apical and near apical tissue with prostate cancer and prostatic involvement by the bladder transitional cell carcinoma (TCC) is reported to be high. These findings attract attention to the apical resection margin in radical cystoprostatectomy as an area where incomplete excision of cancer may be a more common problem than other anatomical locations. The aim of this study was to evaluate the rate of incidental prostate adenocarcinoma in patients undergoing radical cystoprostatectomy for muscle-invasive bladder cancer and to imply the importance of removal of all prostatic tissue at radical cystoprostatectomy to prevent the residual disease. Materials and Methods: From 2002 to 2004, 55 patients who underwent radical cystoprostatectomy for muscle-invasive bladder cancer were studied retrospectively. Four patients were excluded because of inadequate data and 1 patient was excluded because of known or suspected prostate cancer. A total of 50 patients were included in the study. All patients had no evidence of prostatic malignancy on preoperative clinical assessment and underwent radical cystoprostatectomy with removal of all prostatic tissue including the apex. Of these 50 patients 11 (22%) had orthotopic bladder replacement with intestinal reservoirs and 39 (78%) had ileal conduit. Results: A total of 5 unsuspected adenocarcinomas of the prostate were identified in 50 patients, for an incidence of 10 percent. Mean age of the patients with prostate cancer (70.2 years) was greater than those without prostate cancer (62.0 years). Of these 50 patients 7 (14%) had prostatic intraepitelial neoplasiz (PIN), 2 of 7 patients were in group with unsuspected prostate adenocarcinoma. Additionally, 9 patients had TCC metastasis to prostate (18%). All patients with unsuspected cancer had Gleason score of 3+3=6. There was no evidence of full thickness penetration of the prostatic capsule in any of the 5 patients. Similarly, no evidence of seminal vesicle involvement or metastasis to lymph nodes was found in any of the specimens. Conclusion: Preservation of apical prostatic tissue to improve urinary continence and sexual function postoperatively is not advisable if a significant number of bladder cancer patients are expected to have incidental prostate cancer. Since apex is the most common site, with mapping studies showing 41-75% involvement of the apical and near apical tissue with prostate cancer and an additional 5-43% prostatic involvement by the bladder TCC, we suggest complete removal of prostate at radical cystoprostatectomy for bladder cancer. Additionally, because of the association between these cancers, the high coincidence of cancers of the bladder and prostate must always be kept in mind and should be followed closely for the detection of latent prostate adenocarcinoma.