Hippocampal sulcal cavities are usually considered incidental findings on brain MRI. In a group of 92 elderly volunteers, the authors graded the number and size of hippocampal sulcal cavities with brain MRI to obtain a cavity score. Cavity scores increased with age, and were higher in subjects carrying the APOE epsilon4 or epsilon2 alleles than in subjects with the epsilon3/3 genotype. Age-related morphologic changes in the hippocampus may be mediated by the APOE genotype.