BACKGROUND: chronic kidney disease (CKD) is a pathology for which the prevalence increases with age but it remains uncertain whether this is due to ageing. METHODS: all patients at least 50 years old with at least two creatinine measurements in a primary care-based morbidity registration network were selected. The patients were divided into stages of CKD using two eGFRs calculated by the MDRD equation. The mean eGFR for different age groups and the decline with increasing age was calculated. RESULTS: in total, 34,642 patients, of whom 18,644 were women, were included. The mean age was 69 years and the mean eGFR decreased from 84Â ml/min at age 50-54 to 52Â ml/min at age 95+. The prevalence of an eGFR <Â 60Â ml/min increased from 5.4% at age 50-54 years to 73% at age 95+. The prevalence of an eGFRÂ <Â 30Â ml/min increased from 0.4% at age 50-54 to 12% at age 95+. Of the patients aged 80-90 years old, 52% has an eGFR Â >Â 60Â ml/min. CONCLUSION: the prevalence of CKD increases with age and despite the decline of the mean eGFR with ageing almost half of the oldest old has an eGFR Â >Â 60Â ml/min.