Background: Operating room efficiency is a major determinant of hospital cost. Maximizing throughput, while maintaining quality, is therefore paramount to maintenance of financial viability. Cancellation of surgery may increase a hospital's cost and affect the efficiency of operating room and waste of resources. This study was conducted to determine the rate and causes of canceled surgeries, and identifies areas for improvement in a teaching hospital in Tehran.

Material & Methods: We carried out a descriptive study of the reasons for canceling scheduled operations. Data were collected during 9 consecutive months. The reasons for cancellation were identified by theatre staff. We grouped all the reasons into 13 reasons. Other necessary information like operated surgery was obtained from IT department. Descriptive statistics (frequency, percentage, 95% confidence interval) were used to analyses of data.  Statistical analyses were performed using SPSS and Excel Microsoft office.

Results: in this study, 18.2% of the 3381 scheduled operation were canceled on the day of surgery, 32.1% of them because of vascular surgery, followed by orthopedics (18.7%), general surgery (15.5%) and nose and throat surgery (13.7%). The common reasons for cancellation were lack of theatre time, clinical change in the patient's condition, lack of paraclinic tests and consultant's report on patient flow problems, blood preservation, drug and necessary equipment for surgery. 

Conclusion: This study demonstrated that most cancellations of scheduled operation are due to hospital deficiencies and medical team reasons that most of them are preventable. Several changes like better infrastructural facilities, enhanced interdepartmental communication are suggested to try and reduce the cancellation rate.