Delirium, an acute decline in attention and cognition, occurs among hospitalized patients at rates estimated to range from 14% to 56% and increases the risk for morbidity and mortality. The purpose of this systematic review was to evaluate the effectiveness and safety of in-facility multicomponent delirium prevention programs. A search of 6 databases (including MEDLINE, EMBASE, and CINAHL) was conducted through September 2012. Randomized, controlled trials; controlled clinical trials; interrupted time series; and controlled before-after studies with a prospective postintervention portion were eligible for inclusion. The evidence from 19 studies that met the inclusion criteria suggests that most multicomponent interventions are effective in preventing onset of delirium in at-risk patients in a hospital setting. Evidence was insufficient to determine the benefit of such programs in other care settings. Future comparative effectiveness studies with standardized protocols are needed to identify which components in multicomponent interventions are most effective for delirium prevention.