Associations of sleep characteristics with mild cognitive impairment (Mci) have been examined in cross-sectional, but rarely in longitudinal studies. incident Mci and sleep characteristics were assessed in 1,890 participants of the first and second follow-up of the Heinz Nixdorf Recall study, a populationbased cohort study in Germany (age at first follow-up 50−80 years, mean follow-up 5.2 years). MCI was assessed with extensive cognitive tests. Sleep questionnaires including pSQi (pittsburgh Sleep Quality index) were used to assess sleep quality, sleep disturbances, time asleep, and time in bed. Relative risks (RR) of developing Mci when exposed to sleep characteristics were assessed in regression models adjusted for sociodemographic and cardiovascular risk factors. poor sleep quality (pSQi > 5) (RR = 1.43, 95% CI: 1.12−1.82, fully adjusted, reference: PSQI ≤ 5) and difficulties initiating sleep (almost nightly versus never) (RR = 1.40, 0.94−2.08) were associated with incident MCI. For time in bed, the risk of MCI was increased for ≤ 5 hours (RR = 2.86, 1.24─6.60, reference:7 to <8 hours). In this longitudinal study with older participants, MCI risk was increased in persons with poor sleep quality, difficulties initiating sleep, and short time in bed. Dementia is a growing public health burden worldwide. In 2013 an estimated 44.35 million persons had a prevalent dementia 1. By 2050 it is expected that this number triples to 135.46 million prevalent dementia cases 2,3. Because no effective causal medical therapies are available for dementia, primary prevention of dementia and of its early precursors is the most promising option currently available to cap the rising prevalence 4,5. Subjects with mild cognitive impairment (MCI) have an increased risk of progression to Alzheimer's disease (AD) and other forms of dementia. Therefore, identification of modifiable risk factors for incident MCI is important, and poor sleep is considered a potential risk factor for cognitive decline and disease progression 6-13. Sleep characteristics were suggested as modifiable risk factors for cognitive decline, for example by influencing hippocampal volume 14,15. Two up-to-date reviews on this relationship indicate an association between cognitive decline and sleep problems, such as poor sleep quality, short or long sleep duration, and sleep disturbances 12,16. However, both reviews concluded that there is still a need for long term prospective studies to ensure that sleep problems precede cognitive decline 12,16. Two recently published cohort studies on sleep characteristics and dementia were not included in these reviews 17,18. Both suggest that self-reported long sleep duration as well as self-reported sleep disturbances increase the risk of dementia. Additionally, Jackowska and Cadar 19 found an association between decreased cognitive function and self-reported long and short sleep duration in their