BackgroundSleep disturbances resulting from adverse clinical and environmental conditions are associated with unfavourable outcomes in critically ill patients.AimTo collect evidence on the effect of dark nighttime interventions on sleep quality and daytime sleepiness in intensive care unit (ICU) patients.Study DesignThe study followed the Preferred Reporting Items for Systematic reviews and Meta‐Analyses recommendations. This is a systematic review and meta‐analysis of experimental and quasi‐experimental studies, developed with adult patients admitted to ICUs and submitted to measures such as environmental brightness reduction, eye mask or blue light‐blocking glass use at night. Outcomes were subjective or objective sleep quality and excessive daytime sleepiness. Search was carried out in the PubMed/MEDLINE, Cochrane Library, Embase, Virtual Health Library, Cumulative Index to Nursing and Allied Health Literature, Web of Science, and Scopus databases, using grey literature. Covidence software, Cochrane tools and Grading of Recommendations Assessment, Development and Evaluation were used, and a meta‐analysis was performed using RevMan software.ResultsThirteen articles were included in the systematic review and seven studies were included in the meta‐analysis. There were 3 trials with 175 participants regarding lighting reduction and environmental noise control versus the usual routine, 2 of these trials, with 96 patients, were compiled in meta‐analysis in which it was observed a significant statistical improvement in subjective sleep quality, mean difference (MD) of 11.89 points (0–100); 95% confidence interval (CI) 8.0–15.76, evidence set with moderate certainty, as well as this same intervention, reduced daytime sleepiness in 2 trials, 135 participants (standardized MD −0.63; 95% CI −0.98 to −0.28), with low certainty evidence. Eye masks versus usual routine, 2 trials, 126 participants, improved subjective sleep quality (MD of 10 points; 95% CI 7.97–12.03), with moderate certainty of evidence. Eye mask use combined with other therapies versus usual routine, 5 trials, 204 participants, improved subjective sleep quality in all studies, with low certainty of evidence. Objective sleep assessment was not improved with these interventions.ConclusionThis review shows some benefits of nighttime interventions on subjective sleep quality and excessive sleepiness, however, there is an urgent need to conduct better and more robust studies in this field.Relevance to Clinical Practiceapplying measures such as lighting reduction and eye mask use significantly improves sleep quality.