Estimated glomerular filtration rate (eGFR) was used for analysis of kidney disease prevalence in the United States. The study investigated on prevalence, associated disorders, and kidney disease awareness in an Italian population sample. Data were collected on serum creatinine, other laboratory indices, blood pressure, and medical history in the Gubbio Population Study (n=4574, both sexes, ages 18-95 years). Analyses were carried out on eGFR (equation of Modification Diet in Renal Disease study), disorders potentially secondary to kidney dysfunction (hypertension, high serum uric acid, high serum phosphorus/low serum calcium, high serum potassium, cardiovascular disease, anemia), and kidney disease awareness. The prevalence of eGFR <60 ml/min x 1.73 m(2) increased with age in both sexes (from <1% for ages 18-24 years to >30% for ages > or =75 years, P<0.001). In the group with eGFR <60 ml/min x 1.73 m(2), number of disorders secondary to kidney dysfunction was > or =2 in the majority of persons, was higher than in persons with eGFR > or =60 ml/min x 1.73 m(2) (P<0.001), and was inversely related to eGFR (P<0.001). The prevalence of reported kidney disease was 3.3% in the group with eGFR <60 ml/min x 1.73 m(2) and directly related to serum creatinine and number of disorders secondary to kidney dysfunction (P<0.001). Low kidney function is frequent in the older population and is associated with disorders typical of kidney disease. Persons with low kidney function are rarely aware of kidney disease unless of very high serum creatinine or presence of many disorders typical of kidney disease.