['To determine whether mean leukocyte telomere length (LTL) serves as a biomarker of disability assessed according to activities of daily living (ADLs) and what factors may modify this relationship.', 'Retrospective cross-sectional study.', 'A subset of the National Long Term Care Survey (NTLCS), a Medicare-based U.S. population longitudinal study focused on trends of overall health and functional status in older adults.', 'Six hundred and twenty-four individuals from the 1999 wave of the NTLCS cohort.', 'Relative LTL determined according to quantitative polymerase chain reaction. LTL has previously been shown to correlate with common age-related disorders and mortality, as well as with socioeconomic status.', 'A sex difference in LTL was observed but not age-dependent shortening or association with socioeconomic status. LTL was associated with disability and functional status assessed according to ADLs. The association between ADLs and LTL was stronger in subjects without diabetes mellitus, whereas associations were not seen when only subjects with diabetes mellitus were analyzed. Associations between LTL and cardiovascular disease (CVD) and cancer were also present in the group without diabetes mellitus but not in the group with diabetes mellitus.'] Is leukocyte telomere length associated with disability in older u.s. Population?