Postoperative bleeding is the most frequent surgical complication after tonsillectomy and may be associated with increased mortality rate. We have, therefore, analyzed factors associated with and prognostic for bleeding after tonsillectomy. The 2,254 patients who underwent tonsillectomy under general anesthesia at our institution from January 2005 to December 2009 were divided into bleeding and non-bleeding groups, and their demographic and clinical characteristics were compared. Age, administration of steroid immediately after general anesthesia, absence of administration of non-steroidal anti-inflammatory drugs, and the surgeon's experience were significantly associated with bleeding. In contrast, gender, chief complaints, performance of associated surgery, and type of anesthetic were not associated with postoperative bleeding. Hemorrhage after tonsillectomy was associated with the administration of steroids and with the non-administration of non-steroidal anti-inflammatory drugs.