Agitation is exhibited by most nursing home residents with dementia and is a risk factor for poor health outcomes. Identifying the antecedents of agitation is essential for appropriate treatment because interventions require well-defined targets. This study explored relationships between level of social interaction (high vs. low), the premorbid personality trait of extraversion, and agitation using baseline data from a clinical trial that tested the efficacy of activity interventions for agitation. Most residents exhibited at least one agitated behavior over the 332 observation days. Agitation was significantly greater under high social interaction as compared with low social interaction (P < .0001) regardless of the extraversion score.