Abstract A battery of 21 standardized neuropsychological tests was used in a retrospective study carried out on 52 mildly demented Alzheimer patients to analyse the relationship between age at onset of disease and the progress of cognitive impairment. Early onset was found to be associated with a more severe impairment. Possible sampling biases are discussed. Forty-seven patients were also tested for hemisphere asymmetry of cognitive impairment with two subsets of tests predominantly tapping left and right hemisphere abilities, respectively. We found a significant predominance of left-sided impairment which was not related to age at onset of disease. Possible relationship of this finding to healthy brain asymmetries is discussed.