Background. Risk factors associated with underprescribing, such as increasing age and dementia diagnosis, are highly prevalent among LTC residents. Despite being recognized as a highly prevalent problem among elderly persons, underprescribing of EBP has not been studied adequately among elderly persons residing in LTC facilities. The objective of this dissertation was to measure the prevalence of EBP prescribing among LTC elderly residents, as well as to determine if disparities in prescribing EBP exist by dementia and cognitive level.;Methods. A longitudinal cohort at the resident-month level was assembled from a nationally representative sample of Medicare LTC residents. Resident-months with a LTC facility stay of two or more consecutive days from January 1st 2000 to December 31 st 2002 were included in the study. Selected resident-months were retrospectively tested for the presence of each one of seven specific conditions needed to be treated with EBP, and subsequently evaluated for the prevalence of EBP prescribing. A generalized estimating equations procedure was used to study the association between dementia diagnosis, level of cognitive impairment, and prescribing EBP.;Results. 1,938 LTC residents were eligible for inclusion. Mean age was 85 years; 72% were female. The highest EBP prevalence was found for the use of a bowel regimen if receiving opioids (73%) and the lowest EBP was found for the use of beta-blockers among residents with CHF (17%). Resident-months with dementia and/or moderate to severe level of cognitive impairment were not statistically significantly associated with EBP. Increasing age (OR=0.78; 95% CI=0.62, 0.98) and higher comorbidity level (OR=0.71; 95% CI=0.52, 0.98) were statistically significantly associated with lower odds of receiving all of the indicated EBP. Conclusion. The prevalence of EBP among US LTC residents is below what is considered to be optimal among those with and without dementia. The EBP therapies tested in this study have been shown to increase quality of life and to decrease hospitalizations and mortality among elderly patients. However, the low prevalence of EBP in this LTC population suggests that complex care issues associated with age give rise to challenges in defining and implementing "best" care approaches.