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Research interest in sleep as a risk factor for dementia has grown, warranting an update in advances over the last 18 months, particularly in the mild cognitive impairment (MCI) stage in which interventions may be best targeted.The current systematic review includes empiric research articles published since 2016 that have investigated sleep (excluding obstructive sleep apnea) in MCI. Published articles include case–control studies, those examining clinical correlates of sleep problems, sleep microarchitecture, neuroimaging studies and novel cerebrospinal and blood-based markers.Evidence accumulated since 2016 continues to demonstrate that people with MCI manifest sleep disturbance on self-report measures. Neurophysiologically, sleep disturbance in MCI appears to be associated with diminished sleep spindles, key processes involved in overnight memory consolidation. Those with both MCI and sleep disturbance appear to have more pronounced functional connectivity alterations in temporoparietal brain regions and higher levels of the wake-promoting neurotransmitter orexin in cerebrospinal fluid than those with MCI alone. Novel findings also suggest that sleep may mediate homocysteine and oxidative stress mechanisms, warranting further exploration. Further studies focusing on novel interventions for sleep and circadian disturbance in MCI are warranted, particularly those targeting sleep spindles, orexin/hypocretin and the oxidative stress system.