Background: Patient safety has become an area of interest in many countries. One of the most important types of patient safety is pressure ulcers that constitute an important sanitary problem that daily affects the patients and the health care systems. Several studies have indicated that nurses' knowledge, perception and practices about pressure ulcer (PU) prevention are inadequate. Therefore, the aim of this study is to assess nurses' knowledge, perception and practices regarding pressure ulcer at the Intensive Care Units (ICUs) of Mansoura Emergency Hospital. Material and Methods: A descriptive exploratory design was used to conduct this study on fifty nurses who involved in providing direct care for critically ill patients in Mansoura Emergency Hospital. Three tools were used for data collection: knowledge questionnaire, perception questionnaire and observation checklist. Results: the findings showed that three quarters of nurses had unsatisfactory knowledge, perception and practice regarding pressure ulcer prevention. Positive correlation was found between nurses' knowledge and perception ( r=.417 , p=.003). In contrast no correlation existed between nurses' knowledge and practices ( r= -.059, p= .682). Conclusion: there is need for continuing education to upgrade nurses' knowledge, increase their perception and improve their practices regarding pressure ulcer prevention. Recommendations: enrichment of nurses' knowledge, perception and practices related to pressure ulcer prevention to be the cornerstone in care of critically ill patients. As well, replication of this study on large probability sample.