Direct amyloid invasion of prostate tissue resulting in massive bleeding may be fatal, and rapid diagnosis is difficult.A 71-y-old male undergoing regular hemodialysis with primary light-chain (AL) amyloidosis was admitted due to gross hematuria for 2days. Cystoscopy revealed oozing from the prostatic urethra. Therefore, electrocauterization was performed, and his symptoms resolved. Unfortunately, he experienced recurrent massive hematuria 3months later. Tests for serum D-dimer and fibrin degradation products were both positive. Followed serum factor X level was low at 5.4%. Gross hematuria persisted despite of blood transfusions, desmopressin, and vitamin K therapy. Emergent cystoscopy revealed oozing from the prostatic urethra, as was found previously. Therefore, electrocauterization and transurethral resection of the prostate were performed. Analysis of a biopsy specimen of prostate demonstrated strong amyloid deposition in the vascular and perivascular regions. Electron microscopy showed relatively straight fibrils with diameters of 7–10nm in the perivascular region. Gross hematuria subsided then, and no recurrence was noted at a 6-month follow-up.Systemic AL amyloidosis can cause potentially life-threatening hemorrhage. Hemostatic defects and direct invasion with amyloid angiopathy are main pathogenic factors. Timely surgical intervention may be imperative.