OBJECTIVE: Weight loss is a common occurrence in Alzheimer's disease (AD). This study was undertaken to investigate the relationship between weight loss and behavioral symptoms in institutionalized AD subjects. DESIGN: Observational study. SETTING: Two facilities that included assisted living and nursing care. PARTICIPANTS: Residents with probable or possible AD (n = 32). MEASUREMENTS: Weight was measured monthly. At baseline, month 3, and month 6, a knowledgeable staff member provided information that included the Neuropsychiatric Inventory: Nursing Home Version (NPI-NH, ie, a measure of behavioral symptoms) and a questionnaire regarding eating habits, food intake, and appetite. Two-day calorie counts were done and accelerometers were worn to monitor physical activity. RESULTS: At baseline, the mean body mass index (BMI) was 24.0 (standard deviation, 3.5) with 12 subjects exhibiting a BMI <22. BMI was negatively associated with the baseline NPI-NH total score (Spearman Correlation Coefficient -0.52, P <0.01), which indicates that subjects with low BMIs were more likely to have higher frequency and severity of behavioral problems. Individual behavior scores for agitation/aggression (-0.40, P <0.05), depression (-0.31, P = 0.08), irritability/lability (-0.47, P <0.01), aberrant motor behavior (ie, pacing, -0.42, P <0.05), nighttime behavior (-0.37, P = 0.05), and appetite/eating (-0.48, P <0.01) at baseline were negatively correlated with baseline BMI. Behaviors not correlated with BMI were delusions, hallucinations, elation, apathy, and disinhibition. Although this was a small sample followed for a relatively short time period, change in specific NPI-NH scores from baseline to month 6 were correlated with the change in weight over the 6-month period. Both agitation/aggression (-0.37, P = 0.05) and disinhibition (-0.45, P <0.05) showed negative correlation with weight change, which indicates an association between changes in these behaviors and weight loss. There were no significant differences between those who lost weight (n = 13) and those who did not (n = 19) on baseline variables, which included age, comorbidity, functional status, and NPI-NH. However, those who lost weight had a significantly higher BMI at baseline than those who gained weight. CONCLUSIONS: These preliminary results suggest that behavioral disturbances play a role in low body weight and weight loss in AD subjects.