The Extended Scale for Dementia (ESD), a development of the Mattis Dementia Rating Scale, has been used in the evaluation of dementia and aging and has shown substantial clinical utility. We report on analyses of its properties and internal structure in three samples of older people: 153 normals, 101 psychiatric hospital residents, and 114 patients with Alzheimer disease. The results showed good internal consistency in the two clinical samples, with much lower reliability in the normals, for whom the test was too easy. A review of the item statistics led to the use of 17 of the 23 ESD items in item component analyses in the three samples. Use of Horn's parallel analysis criterion led to the retention of three components in the normal group and one in both the hospital and Alzheimer groups. The results are compared with other work and are in accordance with the view that cognitive structure becomes more simple with increasing dementia.