Behavioral changes in 44 subjects with well-characterized mild senile dementia of the Alzheimer's type (SDAT) and 16 subjects with only questionable SDAT were compared to a control group of 58 subjects. Answers to both open-ended questions and personality items from the Blessed Dementia Scale were examined. Seventeen items were classified into seven categories by factor analysis and then further categorized into four clinically useful groups: passive, agitated, self-centered, and suspicious. Over 75% of subjects with mild SDAT had behavioral changes compared to 10% of controls. Passive symptoms were the most common, occurring in two-thirds of mild SDAT subjects. Agitated and self-centered symptoms were also common, occurring half as frequently as passive symptoms. Passive symptoms occurred alone in 25% of those with mild SDAT, whereas passive symptoms, together with agitated and/or self-centered symptoms, were present in 11-16% of subjects with mild SDAT. Agitated or self-centered symptoms rarely occurred alone. Characterizing the behavioral symptoms of SDAT is important for their clinical implications and for an approach to understanding brain-behavioral relationships.