Tehran University of Medical Sciences Journal of Modern Rehabilitation 2538-385X 10 1 2016 08 28 35 42 EN Mohammad Reza Khami Assistant Professor, Department of Community Oral Health, Research Center for Caries Prevention, Tehran University of Medical Sciences, Tehran, Iran. Samaneh Razeghi Community Oral Health, Research Center for Caries Prevention, Tehran University of Medical Sciences, Tehran, Iran. Seyed Mahdi Mirmohammadi Dentist, Medical Laser Research Center, ACECR, Tehran, Iran. 2016 08 28 2016 08 28 Introduction: Prevention and control of cross infections for the personnel of dental offices and clinics are a critical issue in dental practice. In this study, a standardized questionnaire was developed to assess the knowledge, attitude and practice of the oral health-care workers in Tehran University Dental School regarding the blood-transmitted diseases and its validity and reliability were determined. Material and Methods: The draft of the questionnaire was assessed by two experts and the necessary corrections were done. The questionnaire content validity was measured by 10 faculty members of Tehran University Dental School regarding relevance, simplicity, clarity, and importance of the questions. Furthermore, the reliability of the questions was assessed by 21 dental nurses. Inter-rater agreement (IRA) values were reported by both the conservative and less conservative approaches for the relevance, simplicity, clarity, and importance. Content validity items and the percentage of the reliable questions were determined according to the nurses’ responses to each question. Results: Content validity values were 90.24%, 73.17%, 73.17% and 39.02% for the relevance, simplicity, clarity and importance, respectively, using the general consensus approach. IRAvalues in two conservative and less conservative approaches were 90.24% and 92.68% for the relevance; 73.17% and 85.37% for the simplicity; 73.17% and 85.37% for the clarity, and 39.02% and 51.22% for the importance, respectively. The percentage of reliable questions was within the range of 80.9-100%. Conclusion: The questionnaire had acceptable reliability. https://jmr.tums.ac.ir/index.php/jmr/article/view/7 https://jmr.tums.ac.ir/index.php/jmr/article/download/7/16