BACKGROUND: Physical restraint is among the commonly used methods for ensuring patient safety in intensive care units. However, nurses usually experience ethical dilemmas over using physical restraint because they need to weigh patient autonomy against patient safety. AIM: The aim of this study was to explore factors behind ethical dilemmas for critical care nurses over using physical restraint for patients. DESIGN: This is a qualitative study using conventional content analysis approach, as suggested by Graneheim and Lundman, to analyze the data. METHODS: Seventeen critical care nurses were purposefully recruited from the four intensive care units in Tehran, Iran. Data were collected through in-depth semi-structured interviews and were concurrently analyzed through conventional content analysis as suggested by Graneheim and Lundman. ETHICAL CONSIDERATION: This study was approved by the Ethics Committee of Iran University of Medical Sciences, Tehran, Iran with the code: IR.IUMS.REC.1397.795. Before interviews, participants were provided with explanations about the aim of the study, the confidentiality of the data, their freedom to participate, and the right to withdraw the study, and their free access to the study findings. Finally, their consents were obtained, and interviews were started. RESULTS: Factors behind ethical dilemmas for critical care nurses over using physical restraint were categorized into three main categories, namely the outcomes of using physical restraint, the outcomes of not using physical restraint, and emotional distress for nurses. The outcomes of using physical restraint were categorized into the three subcategories of ensuring patient safety, physical damage to patients, and mental damage to the patient. The outcomes of not using physical restraint fell into two subcategories, namely the risks associated with not using physical restraint and legal problems for nurses. Finally, the two subcategories of the emotional distress for nurses main category were nurses' negative feelings about restraint use and uncertainty over the decision on physical restraint use. CONCLUSION: Decision-making for restraint use is often associated with ethical dilemmas, because nurses need to weight the outcomes of its use against the outcomes of not using it and also consider patient safety and autonomy. Health authorities are recommended to develop clear evidence-based guidelines for restraint use and develop and implement educational and counseling programs for nurses on the principles of ethical nursing practice, patient rights, physical restraint guidelines and protocols, and management of emotional, ethical, and legal problems associated with physical restraint use.