Background: Delirium is a common and distressing complication of a range of stressor events including infection, new medications and environment change that is often experienced by older people with frailty and dementia. Older people living in institutional long-term care (LTC)are at high risk of delirium, which increases the risk of admission to hospital, development of or worsening of dementia, and mortality.Delirium is also associated with substantial healthcare costs. Although it is possible to prevent delirium in the hospital setting by providing multicomponent delirium prevention interventions it is currently unclear whether interventions to prevent delirium in LTCare effective.Objectives: To assess the effectiveness of interventions for preventing delirium in older people in long term care.Search methods: We searched ALOIS (www.medicine.ox.ac.uk/alois) - the Cochrane Dementia and Cognitive Improvement Group's Specialised Register- on 23 April 2013. The search was as sensitive as possible to identify all studies on ALOIS relating to delirium. We ran additional separate searches in major healthcare databases, trial registers, the Cochrane Central Register of Controlled Trials (CENTRAL) and grey literature sources, to ensure that the search was as comprehensive as possible.Selection criteria: We included randomised controlled trials (RCTs) and cluster-randomised controlled trials (cluster-RCTs) of single- and multi componentn on-pharmacological and pharmacological interventions for preventing delirium in older people (aged 65 years and over) in permanent LTC residence.Data collection and analysis: Two independent review authors examined the titles and abstracts of citations identified by the search for eligibility and extracted data, with any disagreements settled by consensus. Primary outcomes were prevalence, incidence and severity of delirium. Secondary outcomes included new diagnosis of dementia, activities of daily living, quality of life and adverse outcomes. We used risk ratios (RRs)as measures of treatment effect for dichotomous outcomes and hazard ratios (HR) for time to event data.Main results We included two trials that recruited 3636 participants.Both were complex single-component non-pharmacological delirium prevention interventions. Risk of bias for many items was unclear due to inadequate reporting. Notably, there was no evidence of blinding of trial participants or assessors in either trial. One small cluster-RCT (n = 98) of a hydration-based intervention reported no reduction in delirium incidence in the intervention group compared to control (RR 0.85, 95% confidence interval (CI) 0.18 to 4.00, analysis not adjusted for clustering, very low quality evidence). Results were imprecise and there were serious limitations evident in trial design.One large cluster-RCT (n = 3538) of a computerised system to identify medications that may contribute to delirium risk and trigger a pharmacist-led medication review reported a large reduction in delirium incidence (12-month HR 0.42, CI 0.34 to 0.51, moderat equality evidence) but no clear evidence of reduction in hospital admissions (HR 0.89, CI 0.72 to 1.10, moderate quality evidence), in mortality (HR 0.88, CI 0.66 to 1.17, moderate quality evidence) or in falls risk (HR 1.03, CI 0.92 to 1.15, moderate quality evidence).Authors' conclusions Our review identified very limited evidence on interventions for preventing deliriumin older people in LTC. Introduction of a software based intervention to identify medications that could contribute to delirium risk so that a pharmacist-led medication review and monitoring plan can be initiated may reduce incidence of delirium for older people in institutional LTC. This is based on one large RCT in the United States and may not be practical in other countries which do not have comparable information technology services available in care homes. Our review identified only one ongoing pilot trial of a multicomponent delirium prevention intervention and no trials of pharmacological agents. Future trials of computerised medication management systems and multicomponent non-pharmacological and pharmacological delirium prevention interventions for older people in LTC are needed to help inform the provision of evidence based care for this vulnerable group.