OBJECTIVES: Understanding rating scale properties is essential in using instruments to determine clinically important differences associated with disease treatments and determining their value. This study seeks to determine whether the Behavior Pathology in Alzheimer's Disease Frequency Weighted Severity Scale (BEHAVE-AD-FW) measures symptoms of dementia distinct from cognitive function. METHODS: Baseline data on 215 outpatients with probable AD in a randomized, double-blind, placebo-controlled clinical trial. Higher scores on the BEHAVE-AD-FW total score and category scores (paranoid/delusions; hallucinations; activity disturbance; aggression; diurnal rhythm variation; affective disturbance; anxieties/phobia) indicate more pathological behavior. Pearson correlations were used to correlate the BEHAVE-AD-FW (total score and category scores) with cognitive function as measured by the Alzheimer's Disease Assessment Scale - cognitive subscale (ADAS-cog) and Mini Mental State Exam (MMSE). RESULTS: Mean age was 75.12 years and the percentage female was 57.94%. At baseline, the mean (standard deviation, sd) scores of cognitive function reflected a population with mild AD: ADAS-cog, 21.88 (8.65;), MMSE, 19.77 (3.67). The BEHAVE-AD-FW total score range was 0 to 25; its mean (sd) and median were 4.10 (4.68) and 3. Seven sub-scales of BEHAVE-AD-FW display significant levels of symptoms (p<0.005). Although statistically significant and in the expected direction, the magnitude of the correlations of the total score of the BEHAVE-AD-FW with ADAS-Cog (r=0.22) and MMSE (r=-0.19), was relatively low. Correlations of ADAS-Cog and MMSE with category scores were highest with paranoid/delusions (r=0.25, ADAS-Cog; r=-0.16, MMSE) and activity disturbances (r=0.25, ADAS-Cog; r=-0.25, MMSE). The weakest relationships, not statistically significant, were found on aggressiveness (r=0.01, ADAS-Cog; r=-0.06, MMSE) and diurnal rhythm (r=-0.12, ADAS-Cog; r=0.09, MMSE). CONCLUSIONS: Given the relatively low correlations (r <0.40) of the BEHAVE-AD-FW with ADAS-Cog and MMSE, the BEHAVE-AD-FW may measure previously undetected symptoms of dementia in AD and might be an independent supplement to measures of cognition.