Background: Sleep is essential for well-being and recovery from illness. The critically ill are in significant need of sleep but at increased risk of sleep loss and disruption. Objectives: To determine the quality and duration of sleep experienced by adults who are patients in intensive care units and factors affecting their sleep. Design: An integrative approach was used for this literature review in order to explore the available evidence on this topic, which has yet to be fully investigated. Data sources: PubMed, CINAHL, Psychinfo, the Australian Digital Theses Program and ProQuest Dissertations and Theses (Interdisciplinary) databases were searched for studies conducted about sleep in adult intensive care units. Manual searches of papers identified from this search were performed to find additional studies. Review methods: Data related to the quality and duration of sleep along with study design, sample size and intensive care context were extracted, evaluated and summarised. Results: Total sleep time is normal or reduced with significant fragmentation. Light sleep is prolonged and deep and rapid eye movement sleep are reduced. The most likely factors affecting sleep quality are high sound levels, frequent interventions and medications. Data obtained from polysomnography are supported by patient self reports. Considerable variation in data exists between patients and studies affecting generalizability. Existing criteria for staging sleep may be inadequate for quantifying sleep in intensive care patients. Conclusions: There is evidence that intensive care patientsâ sleep is significantly disrupted. Alternative methods of quantifying sleep for intensive care patients may be required. Few large observational or interventional studies have used polysomnography and simultaneous recordings of intrinsic and extrinsic disruptive factors. These studies are required in order to improve sleep for intensive care patients.