Frailty is an important geriatric syndrome characterized by multisystem dysregulation. Substantial evidence suggests heightened inflammatory state and significant immune system alterations in frailty. A heightened inflammatory state is marked by increases in levels of inflammatory molecules (interleukin 6 and C-reactive protein) and counts of white blood cell and its subpopulations, which may play an important role in the pathogenesis of frailty, directly or through its detrimental influence on other physiologic systems. Alterations in the innate immune system include decreased proliferation of the peripheral blood mononuclear cells and upregulated monocytic expression of specific stress-responsive inflammatory pathway genes. In the adaptive immune system, although little information is available about potential B-cell changes, significant alterations have been identified in the T-cell compartment, including increased counts of CD8+, CD8+CD28-, CCR5+T cells, above and beyond age-related senescent immune remodeling. Copyright © 2011 Elsevier Inc. All rights reserved.