A case is reported here of a patient with a giant multilocular prostatic cystadenoma who presented with gross hematuria and underwent extensive surgical resection. A 35-year-old man presented with asymptomatic gross hematuria. Magnetic resonance imaging of the pelvis demonstrated a multilocular mass replacing the prostatic gland. At exploration the urinary bladder was found to be displaced anterolaterally and severely adherent to the large tumor. The pathological features were consistent with multilocular prostatic cystadenoma. There have been no signs of tumor recurrence during 24 months' follow-up after surgery. Although the natural history of prostatic cystadenoma remains unknown, complete surgical excision may not always be necessary. Physicians should at least be aware of the possibility of this disease entity before making treatment decisions.