Blood transfusion, like any effective therapy, involves an element of risk. In order to reduce such risks to a maximum, a legislative and statutory framework has been set up. A reliable evaluation of this system is necessary together with an efficient evaluation method whose aim is to guarantee quality service. Favouring the development of the evaluation of professional practices is one of the priorities of the National Agency of Accreditation and Evaluation in Health (ANAES) created in April 1996. Following the recommendations from ANAES, the University Hospital of Brest decided to set up an evaluation of blood transfusion chain from the prescription of blood products to the transfusion act and follow-up of receivers in two health care services. The method used for this evaluation was a clinical audit. It is a method of evaluation, which allows with the help of certain criteria, care practices to be compared to accepted references, in order to measure the quality of these practices and the results of hospital care, so that improvements may be added. We present here the method and results of this evaluation, as well as the improvements we have put in place.