Qualitative features of the neuropsychological test performance of individuals with dementia of the Alzheimer type (DAT) were examined in a population-based study. Qualitative error scores were derived from measures of verbal and figural memory, verbal fluency and confrontation naming for 38 patients with clinically diagnosed DAT, 236 normal elderly (NE) individuals, and 72 others who were questionably demented and at risk (AR) for DAT. Persons with DAT made a greater proportion of intrusion and perseverative errors, and more lexical and semantic naming errors, than the NE participants. These measures provided fair specificity but poor sensitivity for the diagnosis of DAT, and a logistic model based on these measures correctly classified 98% of the NE participants, but only 29% of the DAT participants. The AR participants demonstrated a pattern of errors that was highly similar to that of the DAT patients, and when their scores were subjected to the logistic model, 90% were classified as NE and 10% as DAT. These results indicate that specific error types that have been associated with DAT in self-referred or clinic-based samples also occur in the general population to a greater degree in individuals with DAT or questionable dementia than in NE individuals. Furthermore, these qualitative features may have some diagnostic usefulness in that their presence provides reasonable specificity for DAT or questionable dementia. (JINS, 1997, 3, 387–393.)