The paper deals with the use of estimated glomerular filtration rate (eGFR) as marker of low kidney function in the population. Data were collected on serum creatinine, other laboratory indices, blood pressure, and medical history in a population sample of 2083 men and 2491 women aged between 18-95 years. Estimated GFR was calculated by the equation of Modification Diet in Renal Disease study. Disorders included in the analysis were hypertension, cardiovascular disease, high serum uric acid, high serum phosphorus/low serum calcium, anemia, and high serum potassium. Prevalence of low eGFR (eGFR <60 mL/min per 1.73 m2) increased with age: from <1% for ages 18-24 to >30% for ages > or =75, P<0.001. On the basis of these data, prevalence of low eGFR in the adult Italian population was 5.7% for men (n=1.3 million, 95%CI = 1.1/1.5) and 6.2% for women (n=1.5 million, 95%CI = 1.3/1.8). Disorders associated with kidney dysfunction were two or more in the majority of persons with low eGFR and were more frequent with lower eGFR (p<0.001). Previous diagnosis of kidney disease was reported by less than 5% in people with low eGFR and was progressively higher with higher serum creatinine or with number of associated disorders (p<0.03). Hypertension tended to be more frequently treated but not more frequently controlled in people with low eGFR. Data support the use of eGFR to identify people with or at risk of low kidney function. Awareness of kidney disease is low in people with low eGFR unless serum creatinine is very high or they have many associated disorders.