BACKGROUND: An elective operation is cancelled by many causes. Cancellation of the operation bothers patients physically and emotionally; also it affects the patient's family emotionally. If we know the causes of cancellation, we can prevent them. In addition we can provide better quality medical service. METHOD: We examined all patients scheduled for an operation in An - am Hospital, Korea University from August 3rd, 1999 to September 19th, 1999 and from September 16th, 1999 to December 6th, 1999. We counted the number of operations which were cancelled on the day of operation and put together the causes of cancellation after asking surgical employees. RESULTS: The total numbers of scheduled patients was 2,494 and cancelled patients was 512. The overall cancellation rate was 20.5%. The most common cause was departmental, 48.4%; abnormal laboratory results, 24.8%; patients denial, 9.6%; inadequate preparation, 7.0%; overtime, 5.5%; or a change to local anesthesia, 4.7%. In the departmental causes, 52% was due to an excessive schedule (129/248); 32.3% to delayed admission (80/248); 8.9% to clerical error (22/248); 4.4% to operator problems (11/248); and 1.6% to delayed transfer (4/248). In the abnormal laboratory results, 27.6% were due to the medical causes (35/127); 23.6% to LFT (30/127); 23% to an EKG (23/127); 18% to a chest roentgenogram (18/127); 8.7% to a URI (11/127); and 5.5% to hypertension (7/127). CONCLUSIONS: Overall the cancellation rate of elective surgery was 20.5%. The most common cause was departmental (48.7%), and abnormal laboratory results (24.8%) was next.