Younger patients with glioblastomas have a significantly better prognosis than do older patients. To determine whether patient age might be related to proliferation of glioblastoma cells, glioblastomas from patients of different ages were stained with the Molecular Immunology Borstel number 1 antibody to detect proliferating cells. Younger patient age was a significant predictor of a low Molecular Immunology Borstel number 1 proliferation index (p = 0.0001). This previously unreported association favors an intrinsic difference in the type of glioblastomas that afflict younger patients.