BACKGROUND: Little is known about normal kidney function level and the prognostic significance of low estimated glomerular filtration rate (eGFR) in the elderly. METHODS: We determined age and sex distribution of eGFR with both the Modification of Diet in Renal Disease (MDRD) study and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations in 8705 community-dwelling elderly aged >/= 65 years and studied its relation to 6-year mortality. In a subsample of 1298 subjects examined at 4 years, we assessed annual eGFR decline and clinically relevant markers including microalbuminuria (3-30 mg/mmol creatinine) with diabetes, proteinuria >/= 50 mg/mmol, haemoglobin <11 g/L or resistant hypertension despite three drugs. RESULTS: Median (interquartile range) MDRD eGFR was 78 (68-89) mL/min/1.73 m(2) in men and 74 (65-83) in women; there were 79 (68-87) and 77 (67-85) for CKD-EPI eGFR, respectively. Prevalence of MDRD eGFR <60 mL/min/1.73 m(2) was 13.7% and of CKD-EPI eGFR was 12.9%. After adjustment for several confounders, only those with an eGFR <45 mL/min/1.73 m(2) had significantly higher all-cause and cardiovascular mortality than those with an eGFR of 75-89 mL/min/1.73 m(2) whatever the equation. In the subsample men and women with an MDRD eGFR of 45-59 mL/min/1.73 m(2), 15 and 13% had at least one clinical marker and 15 and 3% had microalbuminuria without diabetes, respectively; these percentages were 41 and 21% and 23 and 10% in men and women with eGFR <45, respectively. Mean MDRD eGFR decline rate was steeper in men than in women, 1.75 versus 1.41 mL/min/1.73 m(2)/year. CONCLUSIONS: Moderately decreased eGFR is more often associated with clinical markers in men than in women. In both sexes, eGFR <45 mL/min/1.73 m(2) is related to poor outcomes. The CKD-EPI and the MDRD equations provide very similar prevalence and long-term risk estimates in this elderly population.