Using a retrospective data analysis, the authors investigated the relationships between instrumental activities of daily living (IADLs) and neuropsychiatric symptoms, cognitive impairment, and medical illness burden in patients with Alzheimer's disease (AD). One hundred forty-three patients fulfilling the clinical criteria for probable or possible AD in an outpatient clinic were assessed for IADLs, neuropsychiatric symptoms, cognitive impairment, and medical illness burden with the Functional Activities Questionnaire (FAQ), Neuropsychiatric Inventory (NPI), Mini-Mental State Exam (MMSE), and Cumulative Illness Rating Scale-Geriatric (CIRS-G). Both MMSE and NPI scores related significantly to IADLs as measured by the FAQ. Several psychiatric symptoms were correlated significantly with IADLs. FAQ scores had no correlation with CIRS-G. Neuropsychiatric findings also were associated significantly with MMSE and had a weak correlation with CIRS-G scores. IADLs changed with cognition and neuropsychiatric disturbances in AD. Medical illness burden had little influence on functional status and a limited impact on neuropsychiatric symptoms.