Carcinosarcoma of the prostate is a rare neoplasm with malignant epithelial and mesenchymal components. Herein, we report the case of a patient who underwent multiple transurethral resections of the prostate showing adenocarcinoma initially then carcinosarcoma. He underwent a robotic-assisted laparoscopic cystoprostatectomy, bilateral pelvic lymph node dissection, and ileal conduit urinary diversion and was discharged on postoperative day 7. Carcinosarcoma is discussed as an extremely rare malignancy of the prostate, with less than 50 cases reported in the literature. Robotic-assisted radical cystoprostatectomy is also discussed as a new procedure in minimally invasive surgery and as the first reported use for prostatic carcinosarcoma.