Biological age is a better measure of functional capacity than chronological age.1 One of the measures of biological age is telomere length. Telomeres are nucleoprotein complexes that protect chromosome ends from damage. The DNA component of telomeres progressively shortens as biological age increases and thus acts as a read out for ‘miles on the biological clock’. 2 Telomere length progressively shortens as biological age increases. Within health care, ageing is almost exclusively described in terms of chronological age. Recent studies explored using biological age to stratify patients and predict outcomes.3 This project acts as a pilot study to investigate whether biological age is related to intensive care unit (ICU) outcomes and whether ICU patients age biologically at an accelerated rate. This project used blood samples from a previous study where patients underwent cardiac surgery and were admitted to the ICU. Blood samples were obtained before surgery and on days 1, 2, and 3 after surgery. The database contained the following physiological parameters: haemoglobin, urea, creatinine, RIFLE score, length of ICU stay, and whether renal replacement therapy was required. Information on co-morbidities and medication was also provided. DNA was isolated using a Maxwell machine and telomere length determined via quantitative PCR. One hundred and fifty-five blood samples from 46 patients underwent analysis. Telomere length did not differ significantly over the 4 days (P=0.662). No relationship was found between telomere length and any physiological parameter, co-morbidity, or medication. There was a trend towards significance with RIFLE score at day 3 increasing as telomere length decreased, although this was not statistically significant (P=0.09). No relationship between telomere length and the available physiological parameters, comorbidities, or medication was found. Telomere length did not vary during ICU stay. This study was limited by its small sample size. Future studies would benefit from a larger sample size; in addition, blood samples could also be obtained at 6 months after discharge to allow gradual alterations in biological age to be determined. Recent studies give evidence that telomere length is a weak biomarker of ageing,3 and that more meaningful data might be obtained using superior markers, such as CDKN2A expression or expression levels of non-coding RNAs.3