Sarcomatoid carcinoma of the prostate is a rare aggressive tumor, characterized by an intimate admixture of two malignant epithelial and sarcomatoid components. We report the case of a prostate tumour reputed to have a poor outcome, in a 59-year-old man. The radical prostatectomy specimen was completely involved. There were no signs of recurrence or metastasis after 15 months of follow up. The serum PSA values before and after chirurgical treatment were normal. The definition of this tumour as its histogenesis and prognosis is discussed.