Background and Aim: Annually, large amounts of fees that paid by hospitals will not be reimbursed as deductions by health insurances and takes irreparable financial losses to hospitals. The purpose of this study was to determine the amount of deductions imposed on hospital bills of Tehran University of Medical Sciences and their causes related to documentation.

Materials and Methods: The present research was a cross-sectional and descriptive study performed in year 2009 on educational hospitals of Tehran University of Medical Sciences. All deductions reports related to Medical Services and Social Insurance related to year 2008 was collected from Income Unit of hospitals. The amount of deduction of each hospital was extracted and organized in the form of comparative tables. Data was analysed by descriptive statistics and Excel application. Then, the amount, type and causes of annually deduction of each hospital was determined.

Results: Most deductions imposed on inpatient bills have been related to the tests, appliances, medicine, residency, surgeon commission, and anesthesia and for outpatient bills have been related to visit, tests and medicine which most of them have been created due to documentation deficiencies.

Conclusion: Most of deductions are due to unfamiliarity of care staff with documentation requirements of insurance organizations. Therefore it is necessary to use a multi-aspect mechanism including education of documentation principles to staff, supervision on record control in the Medical Record Unit and establishment of a committee by university for related activities.