This study describes the development and validation of the Activities of Daily Living Questionnaire (ADLQ), an informant-based assessment of functional abilities, in patients with probable Alzheimer disease and other forms of dementia. The ADLQ measures functioning in six areas: self-care, household care, employment and recreation, shopping and money, travel, and communication. The ADLQ was administered to 140 caregivers followed longitudinally in the Northwestern Alzheimer's Disease Center. In a subset of 28 participants, the total ADLQ score and each of the subscales were found to be highly reproducible, with average concordance coefficients of 0.86. Concurrent validity was established by comparing the ADLQ with the Record of Independent Living, a previously validated measure of level of dependency in daily living activities. The ADLQ was also compared with other measures of dementia severity on the initial and annual follow-up visits and was found to be significantly and negatively correlated with the Mini-Mental State Examination and positively correlated with the Clinical Dementia Rating Scale. The ADLQ has high test-retest and concurrent validity and is consistent with other measures of temporal decline in patients with probable Alzheimer disease and other forms of dementia.