Background: One of the most common complications of Intensive Care Unit (ICU) is neuromuscular dysfunction due to critical illness, which may cause disuse atrophy. Large number of critically ill patients has severe muscle weakness, which has been named ICU-acquired weakness (ICU-AW). Purpose: The purpose of the study is to assess risk factors for acquired muscle weakness among Critical Ill Patients. Research Design: A descriptive exploratory design was utilized to achieve the purpose of this study. Setting: the study was conducted in the Intensive Care Units (ICUs) in Cairo University Hospital (general, chest and internal medicine ICU). Sampling: A Purposive sample of seventy-five patients admitted to the previous mentioned setting. Instruments: Three instruments were used for data collection. Instrument one: Characteristics of patients. Instrument two: muscle strength scale. Instrument three: - Factors contributing in Intensive Care Unit Acquired Muscle Weakness (ICU-AW) tool. Results: showed that more than half of studied patients had ICU-AW, most studied patients who had muscle weakness were older, abnormal WBCs level than the Non-ICU-AW patients. Administration of corticosteroid was higher in the ICU-AW patients than the Non-ICU-AW patients. There was no statistically significant relation between incidence of ICU-AW and gender, administration of parenteral nutrition and application of positioning, walking exercises. Conclusion: More than half of studied patients developed ICU-AW. The contributing factors of ICU-AW are patient age, abnormal WBCs level, not applying range of motion and chair sitting exercise to ICU patients, administration of corticosteroid. Recommendations: Further research is recommended to study extensively the effect of nutritional status on the incidence of ICU-AW. Also, the incidence of ICU-AW in sedated and unconscious patients' needs to be assessed.