Investigating sleep disturbances among intensive care unit (ICU) patients and its serious consequences is considered a crucial issue for nurses. The need of sleep increases during hospitalization time to preserve energy for the healing process. Previous studies have demonstrated that sleep disturbance is one of the most common complaints of patients in the ICUs, with a prevalence of more than 50%. Although the total sleep time might be normal, the patients' sleep is fragmented and light in the intensive care settings. The main purpose of this review is to generate a clear view of what is known about sleep disturbances among ICU patients as well as to identify the gap in knowledge regarding this issue. This was done by describing, summarizing, clarifying, and evaluating well-selected previous studies about this topic. In addition, this concise review has focused on the prevalence of sleep disturbances in the ICU, factors contributing to poor quality of sleep among ICU patients, and the physiological effects of poor sleep on the patients' prognosis.