The relationship between apolipoprotein E (apoE) genotype and cognitive performance was examined in 200 patients with probable Alzheimer's disease (AD). Differences between composite measures of verbal and nonverbal functioning were used to define asymmetric patterns of cognition. Patients who were homozygous for apoE epsilon4 demonstrated relatively worse nonverbal as compared to verbal cognitive ability. In contrast, participants who were heterozygous for apoE epsilon4 or who possessed no epsilon4 allele demonstrated relatively equivalent verbal and nonverbal cognitive abilities. Although age and dementia severity also contributed to these patterns, apoE genotype appears to have a significant unique contribution to cognitive performance in these individuals. The epsilon4 allele may thus be associated with a specific neurocognitive phenotype among patients with AD, with the overall pattern of cognitive asymmetry dependent upon epsilon4 dose.