As part of an interdisciplinary study of organic dementia, a psychologic test for assessing the degree of dementia--the Extended Scale for Dementia--was developed through the expansion and rescoring of the original Mattis Dementia Scale. Statistical analyses of the 23 test items resulted in a scoring scheme which includes the "weighting" of items for scoring purposes. The test was successfully administered to 90 subjects from 6 hospitals in the London (Ontario) region. With use of the Extended Scale, it was possible to discriminate between dementia and non-dementia groups of psychogeriatric inpatients and to correlate the findings closely with those of another measure of the degree of dementia, viz, the London Psychogeriatric Rating Scale (Ment.). Dementia patients who were retested after 6-month and 12-month intervals showed a significant decline in scores. No significant scoring differences were noted between males and females or between Alzheimer dementia and multi-infarct dementia.