A 39-year-old man complained of the sudden onset of right lower abdominal pain during hemodialysis. His desire for voiding continued even after he excreted 300ml of urine. A urethral catheter was inserted, after which a large volume (3000ml in one hour) of fluid flowed out and his ascites disappeared. Rupture of the urinary bladder was confirmed by cystography. His vital signs were unstable, so he was followed without surgery. Fortunately, the rupture closed spontaneously. An abscess developed near the bladder, but was cured and healed with percutaneous drainage.