Aggressive behavior in persons with dementia who are living in the community was explored in a pilot study using a newly developed instrument, the Ryden Aggression Scale. Factors affecting this kind of research are addressed, including reliability and validity of the instrument, sample bias, diagnostic workup, and control groups. Results of a pilot survey of caregivers revealed aggressive behavior in 65% of a sample of 183 subjects, occurring weekly or more often in 31% and daily in 16%. Verbal and physical aggression were most prevalent (50% and 46%, respectively), while sexual aggression appeared less frequently (18%). Aggression was significantly related to degree of cognitive impairment and prior history of aggressive behavior, but not to diagnosis nor administration of psychotropic medications. Men showed significantly more sexual aggression. Further research to verify these findings is needed.