In this 10-week, double-blind, fixed-dose study, elderly institutionalized patients with dementia and agitation were randomized (3:3:2) to quetiapine 200mg/day, 100mg/day, or placebo. The primary endpoint was change in Positive and Negative Syndrome Scale (PANSS)-Excitement Component (EC) scores at endpoint, analysed using last observation carried forward (LOCF) and observed cases (OC) approaches. Other efficacy measures were the Clinical Global Impression of Change (CGI-C), and response rates (percentage with ≥40% reduction [PANSS-EC]; “much” or “very much improved” [CGI-C]), Neuropsychiatric Inventory-Nursing Home version (NPI-NH), and Cohen-Mansfield Agitation Inventory (CMAI). The key safety measure was incidence of adverse events; change in Mini-Mental State Examination (MMSE) was also assessed. Baseline characteristics of 333 participants (quetiapine 200mg/day, n=117; quetiapine 100mg/day, n=124; placebo, n=92) and completion rates (63-65%) were comparable among groups. Compared with placebo, quetiapine 200mg/day was associated with clinically greater improvements in PANSS-EC (LOCF, p=0.065; OC, p=0.014 [ANCOVA]), CGI-C (LOCF, p=0.017; OC, p=0.002 [ANOVA]), and CGI-C response rates (LOCF, p=0.002; OC, p < 0.001 [Chi-square test]). Quetiapine 100mg/day did not differentiate from placebo on these measures. There were no between-group differences in NPI-NH or CMAI. Incidences of cerebrovascular adverse events, postural hypotension, and falls were similar among groups. MMSE did not change in any group. Mortality was numerically higher in the quetiapine groups; rates were not statistically different from placebo. The results of this study suggest that quetiapine 200mg/day was effective and well-tolerated for treating agitation associated with dementia. However, caution should be exercised given the concerns regarding increased mortality with atypical antipsychotics in this vulnerable patient population.