Background: Sleep disorders other than sleep apnea (non-apnea sleep disorder, NSD), esp. insomnia and excessive daytime sleepiness, has been reported to induce higher risk of cognitive decline and dementia in previous longitudinal follow-up studies. However, large-scale nationwide populationbased study may further confirm the association between NSD and dementia.Methods: It was a nationwide population-based retrospective study. We used data from Taiwan’s National Health Insurance Research Database (NHIRD) between January 2000 and December 2011. The NSD cohort comprised 92,079 patients aged over 20 years with no preexisting dementia. The comparison cohort was propensity-score matched 1:1 with 92079 controls. Incident dementia cases were identified to the end of 2011. The NSD cohort to non-NSD cohort adjusted hazard ratios (aHRs) of dementia were assessed using multivariable Cox proportional hazards regression analysis. Results: Incidence of dementia was 4.19 and 2.95 per 1,000 person-years in the NSD and non-NSD cohorts, respectively, with an aHR of 1.46 (95% CI=1.38–1.54; p<0.0001). Risk of dementia was higher in both gender and whole age subgroup, with slightly higher in men (aHR: 1.48, 95% CI=1.35–1.62, p<0.0001) and in the younger population (aHR: 2.79, 95% CI=1.63–4.78, p<0.0001). Dementia was most likely to occur in the first year of follow-up (aHR: 1.73, 95% CI=1.49–2.02; p<0.0001), but dementia risk remained high 5 years after NSD diagnosis compared to controls (aHR: 1.44, 95% CI=1.32–1.57; p<0.0001). Conclusion: NSD may be an early indicator of decline in cognitive functioning and onset of dementia in the short-term period. It also carries a higher risk for dementia in the long run. Patients with NSD should require close monitoring for cognitive decline.