The progressive decline of renal function with aging is not inevitable, because it is mainly due to comorbid conditions such as hypertension and diabetes. However, in the elderly there is a high prevalence of chronic kidney disease leading to the need for strategies to control cardiovascular risk - death being far more common than dialysis at all stages of kidney function. Serum creatinine, the most widely used surrogate marker of glomerular filtration rate (GFR), is inaccurate with increasing age, particularly in sick and/or malnourished elderly people; it shows the so-called creatinine blind area, and substantial variation between laboratory analytical methods. An alternative endogenous marker is serum cystatin C: it correlates better with renal function and has the potential advantage of improved precision of the assay, but its measurement is still much more expensive. Current guidelines recommend that the 2 most commonly used equations to estimate GFR - the Modification of Diet in Renal Disease Study or Cockcroft-Gault equations - be used to estimate GFR in the clinical setting. Both show relevant bias, with underestimation of GFR in subjects with normal or mild renal impairment, a bias limited by using the more recent Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Nonetheless, keeping in mind that a decreased renal function in the elderly is not benign, current GFR equations facilitate detection, evaluation and management of the disease, and they should result in improved patient care and better clinical outcomes.