Background: Hypothermia is a medical emergency that occurs when the patient loses heat faster than it can be produced. Aim: Identify factors that causing hypothermia and rewarming manoeuver among critically ill patients in Intensive Care Units. Design: A descriptive exploratory research design. Setting: The study was conducted at the intensive care units namely general ICU, trauma ICU , recovery area of surgical and recovery area of orthopedic at Assuit Main University hospital and general ICU and coronary care unit at El-Azhar University hospital. Patients and Method: The study sample consisted of hypothermic patients (=100) and non hypothermic patients (n=130) were included in the study for consecutive six months. Tools were utilized for data collection tool I: patient assessment sheet, tool II hypothermia assessment sheet. Results: study Findings revealed that 99% of hypothermic patients had mild degree of hypothermia and had stage one of hypothermia. Regarding to rewarming manoeuver, it was noticed that 99% of hypothermic patients used rewarming blanket and this were effective in (76.8%) of patients. Conclusion: This study showed that risk factors for hypothermia were diabetes mellitus (hypoglycaemia), underweight and low glasgow coma scale