OBJECTIVES: To estimate the amount of assistance caregivers (CG) of mild to moderate Alzheimer's Disease (AD) patients must provide in a typical day, and to compare those estimates across varying levels of cognition, function or behavior. METHODS: Observational study of 180 patients with mild to moderate AD. Patients were required to have a study partner (CG) who spent at least 10 hours per week with the patient. These results represent an initial analysis of 82 patients enrolled as of January 2007. Estimates of time spent assisting with basic activities of daily living (ADL), instrumental activities (IADL) and supervision during the previous month were collected using the Resource Use in Dementia (RUD)-Lite version 2.3. Total CG time (sum of ADL, IADL, supervision) was assessed across varying levels of cognition (Mini-Mental State Examination, MMSE), function (Disability Assessment of Dementia, DAD), and neuropsychiatric symptoms (Neuropsychiatric Inventory, NPI). RESULTS: Mean patient age was 76.0 years (SD=6.38), compared to 70.9 years (SD=11.26) for caregivers. Caregivers were typically the patient's spouse (74.4%), 56.1% were female, and 75.0% were the sole caregiver. Over one in five CG (18/82) provided more than 8 hours of care / day; support with IADL and supervision accounted for the majority of this time. patients with mild AD (MMSE>21) required a median (mean +/- SD) 1.6 (3.7 +/- 5.74) hours of CG time / day vs 5.9 (8.2 +/- 7.93) hours / day for moderate AD patients (MMSE 15-21), with much of the difference due to IADL and supervision time. Worsening functional (r2=0.19, p<0.0001) and neuropsychiatric status (r2=0.10, p=0.005) were also associated with increased CG time. CONCLUSION: Mild to Moderate AD is associated with significant time burdens for caregivers, with 20% of patients in this study requiring as much as or more than a full working day of support.