Background: Patient safety is an important priority for health care systems. Reports are often published, however, related to errors and adverse events. These have a particularly strong impact when they involve the area of perioperative care. Aim: To investigate: (a) the possible errors and violations of procedures on the part of health professionals from the stage of the arrival of the patient in the operating room until the time of intubation, and (b) to compare the number and type of errors between two hospitals. Method: A descriptive cross-sectional study was conducted in the operating rooms of two Athens hospitals, from February 2008 until April 2009, recording the course of 60 patients who underwent surgery. The sampling strategy used was non-probability sampling. An appropriate questionnaire was used to record data, the development of the content of which was based on the recommendations of the World Health Organization (WHO), the American Association of Food and Drug Administration (FDA), the American Society of Anaesthesiology and a Ministerial decision of the Greek Government about the minimum standards limits for safe anaesthesia. The response rate was 98.6%. The description of quantitative variables was made by mean values and standard deviations and the description of qualitative variables by absolute and relative frequencies.Results: In 18.3% of cases the identity of the patients was not checked at their arrival in the operating room and in 1.7% a false identification was made. In 21.7% of cases the anaesthesiologist did not check the anaesthesia machine before intubation. In 3.4% of the patients a fall off the operating table was recorded, and in 1.7% a burn was caused due to false positioning of the diathermy. In 8.5% of cases the wrong medicine was administrated and in 4.5% perioperative treatment was omitted. In addition, in 30% of the patients an initial assessment of the likelihood of difficult intubation was not made, while 8.5% of them had difficult intubation and 11.9% had complications after intubation. Conclusions: Accepting the inevitability of error and understanding the causative factors can lead to a reduction of the frequency and severity of errors and promote the quality of health care. In the design of a safer health care system the application of error reporting systems will be important to establish safer surgical practice.