A case of müellerian duct cyst with prostate cancer is reported. The patient was a 64-year-old male, complaining of hemospermia. Prostate cancer was suspected by rectal examination and a cystic mass was detected between the ejaculatory ducts by computed tomography and magnetic resonance imaging. He underwent a transperineal needle aspiration of the cyst. The fluid did not contain spermatozoa. A adenocarcinoma was detected from the prostate by needle biopsy. Therefore, a radical prostatectomy with the resection of the cyst was performed. This is the first report about the resection of müellerian duct cyst with the organs around it in Japan.