Malignant tumours of the prostate other than carcinomas are rare. One such malignant tumours arising from the specialised stromal tissue of the prostate is stromal prostatic sarcoma (namely low-grade and high-grade). Herein, we report the clinico-pathological features of a high grade stromal sarcoma of the prostate occurring in a 65-year-old man who presented for urinary obstructive symptoms. The clinical picture suggested a benign prostatic hyperplasia, and surgery consisting in a transcapsular adenomectomy was performed. Following a pathological diagnosis of high grade prostatic stromal sarcoma, a radical cystoprostatectomy and bilateral pelvic node dissection was performed showing residual high grade stromal sarcoma of the prostate and incidental in situ urothelial carcinoma of the bladder. No further medical treatments were planned. One year after surgery the patient is well with no evidence of local disease or distant metastases.