This is a case report of massive hydrohemothorax as a complication of central venous pressure catheterization. This 54 year old male with bladder tumor was anesthetized for surgery of ileal conduit with cystectomy and then a right subclavian vein catheterization was performed, with a supraclavicular approach. Intravenous fluid runned rapidly through G.V.P catheter but no obvious signs of abnormality in the system of C.V.P. catheterization were noted except mild hypotension, tachycardia and gradual increase of C.V.P. during the whole procedure of this operation. The patient had become cyanotic and difficult in respiratio postoperatively, therefore chest X-ray was taken in I.C.U, that showed a massive hydrohemothorax on the side of CV.P. catheter in place. We consequently found that the catheter was misplaced to the right pleural space. About 4500cc of bloody fluid was aspirated with closed thoracotomy and the chest tube was removed 2 days after thoracotomy. Since then all symptoms had been subsided.