Non-urothelial neoplasms of the bladder account for less than 5% of all bladder tumors. Sarcoma constitutes the most usual mesenchymal malignancy of the bladder, with leiomyosarcomas being the most common type of sarcoma in adults. A coexistence of this rare tumor with another malignancy has not been reported, to our knowledge. This report demonstrates a case of high-grade bladder leiomyosarcoma cancer with prostate cancer in a 72-year-old patient. The most striking features of this case include the rapid disease progression that confirms the highly aggressive nature of this uncommon disease.