Background: Prostatic signet-ring adenocarcinoma is a rare histological variant of prostate cancer. The tumor is characterized by an aggressive clinical course. Methods: Herein we present the case of a 78-year-old man with obstructive urinary symptoms and elevated serum prostate specific antigen. Transurethral resection of the prostate was performed. Results: Histologically, a tumor that was mainly composed of signet ring cells was identified. The tumor cells were positive for alcian blue special stain. Another Gleason 4 adenocarcinoma component was identified. The patient received hormonal therapy. A favorable response was documented at 8 months of follow up. Conclusions: Ruling out another primary site of origin, such as the gastrointestinal tract, is mandatory, and a more aggressive management plan should be put in mind.