We report one case of carcinosarcoma of the prostate in a patient of 43 years old. The clinical symptomatology was dominated by pollakiurie, dysuria digestive disorders, oedema of the lower limbs and the alteration of the general status. Digital rectal examination showed a big prostate, hard and irregular. The rate of PSA increased. Echography revealed a pelvic echogenic mass corresponding to a bulky prostate. CT scan of the abdomen and the pelvis showed a tissular, heterogeneous mass of 11 cm occupying the vesicoprostatic space and invading the basis of the bladder and the adjacent muscles (muscles obturateurs internes). Histology of a biopsy fragment of the mass revealed an adenocarcinoma and a mesenchymatous component calling up a prostatic carcinosarcoma. The treatment consisted in chemotherapy VAC. The evolution was deadly after 2 months.