Prostate cancer is extremely rare in men under 35 years of age. The tumour is invariably poorly differentiated and aggressive, with rapidly growing bulky soft tissue metastases and negative tumour markers. Bone metastases develop late and are usually osteolytic. The disease responds poorly to radiation or hormonal therapy and is too advanced at presentation for radical surgery. Chemotherapy appears to be of some benefit, though in the majority of cases death occurs within a year. We describe a 31-year-old man with carcinoma of the prostate. A review of the literature is presented. This is the first patient in whom the epithelial origin of the prostate cancer was confirmed by immunoperoxidase staining with prostatic specific antigen. Plasma prostatic specific antigen was normal despite a large tumour burden and widespread metastases. He did not respond to conventional treatment. The phenotypic expression and biological behaviour of these tumours are distinct from those occurring in men beyond the fourth decade.