Background: This study examines associations between markers of nutritional status and lymphocyte subsets and seeks to determine if lymphocyte profile is predictive of survival in elderly Australians residing in aged care facilities. Aged yet still ambulatory subjects (n = 88, 73 female) living in low-level care and requiring minimal assistance were studied for 143 weeks. At baseline when participants were aged (mean ? SD) 86.0 ? 5.9 years, dietary intake was determined by 3-day weighed food record, body composition was assessed by dual energy X-ray absorptiometry (DXA) and a venous blood sample was taken.Results: At baseline assessment, study participants were consuming nutrient-poor diets and most had symptoms of chronic disease. Although overweight, 40 exhibited sarcopenia. Markers of nutritional status did not relate closely to immune cell numbers (absolute or relative), which on average were within the normal range. Men had lower numbers of CD3+CD4+ cells (CD4+ T cells), a higher proportion of CD3- CD16? CD56? (natural killer (NK) cells) and a higher ratio of NK: CD4+ T cells than women (all P <0.05). The main age-related changes evident were decreased T cells, particularly low CD4+ T cell counts, and increased numbers of CD19+ (B-cell) and NK cells. During the 143 week duration of follow-up, about one quarter of the study participants died, with death more likely in men than women (P <0.01). Poor survival was predicted by the presence of decreased numbers of CD4+ T cells (hazard ratio (HR) 0.919, P <0.01) and expanded numbers of NK cells (HR 1.085, P <0.05) in the blood, and therefore the presence of a high NK: CD4+ T cell ratio (HR 30.521, P <0.01).Conclusions: The NK: CD4+ T cell ratio may potentially have clinical utility for predicting longevity in elderly populations. Further studies are needed in other elderly populations to confirm this finding.