Patients with familial Alzheimer's disease and a subset known to have presenilin mutations were compared with sporadic cases on a comprehensive battery of cognitive tests. These included measures of memory, intelligence, language and perception. The three groups were very comparable, in terms of severity, on global measures of dementia. However, their profiles/patterns of cognitive impairment differed in two respects; the group with sporadic Alzheimer's disease were significantly more impaired on tests of object naming and object perception than either the group with familial Alzheimer's disease or group with familial Alzheimer's disease and presenilin mutations, yet they scored at a significantly higher level on the measure of verbal intelligence. This study provides further evidence of the heterogeneity of the disease process.