The study examines the factor structure and provides test of the discriminative properties of the 38-item Mattis Dementia Rating Scale (MDRS). The MDRS was designed a priori to measure five broad domains of cognitive abilities: attention, initiation/perseveration, conceptualization, construction, and memory. Complete item level data were collected at the USC Alzheimer Disease Research Center from 19 probable Alzheimer's Disease (AD) patients, 17 cases with dementia of various etiologies (e.g., multiple infarct), and 49 contrast subjects. Factor analyses, with rotation to equamax criterion, were performed on education partialled data. Five and six factor solutions accounted for most of the reliable variance and permitted simple structure theoretical description for separate subscales. These factors, similar to Mattis' design, can be characterized as Memory (Recall)/Verbal Fluency, Construction, Memory (short-term), Initiation/Perseveration, and Simple Commands. Cross-validated discriminant analyses performed on five unit-weighted composite variables derived from factor analysis provided better classification (72% vs 62%) than the 38 Mattis items alone.