The study aims to construct and validate a self-administrated questionnaire to assess the patients' perception of patient safety in surgical care units. The originality of the study is to perform sociological interviews of hospitalized patients to assess their own perception on the safety of their care and to create corresponding items which will be included in a new questionnaire. In a second step, patients' perception of patient safety will be assessed in numerous surgical care units in France, in order to analyze the psychometric properties of the questionnaire and consequently to validate the questionnaire. The patients' perception will be compared to the healthcare professionals' perception on patient safety and to the patient safety strategies in place in the care units.