We aimed at verifying whether unrecognized chronic kidney disease (CKD) (i.e., reduced estimated glomerular filtration rate in spite of normal serum creatinine) has prognostic significance in an unselected population of older patients discharged from 11 acute care hospitals located throughout Italy. Our series consisted of 396 participants aged 70 and older. Estimated glomerular filtration rate (eGFR) was calculated by the Modification of Diet in Renal Disease (MDRD) study equation. We compared three groups: Normal renal function (normal serum creatinine levels and normal eGFR), concealed (normal serum creatinine levels and reduced eGFR), or overt (increased creatinine levels and reduced eGFR) renal failure. The relationship between renal function and 1-year mortality was evaluated using Kaplan-Meier curves and Cox regression analysis including potential confounders. Overall, 56 patients died over a cumulative follow-up time of 335 months, with an estimated incidence rate of 16.7/100 person-year (PY). The corresponding figures in patients with normal renal function, concealed CKD, and overt CKD were 9.8/100 PY (95% CI, 5.7-15.7), 28.3/100 PY (95% CI, 13.6-52.1), and 23.0 (95% CI, 15.4-33.0), respectively (log rank test p = 0.006). According to the fully adjusted model, both concealed (hazard ratio [HR], 2.35; 95% CI, 1.09-6.01) and overt CKD (HR, 2.09; 95% CI, 1.05-5.34) were significantly associated with the outcome. Concealed CKD contributes to profile the elderly patient at greater risk of death after being discharged from acute care medical wards. If confirmed in broader populations, this finding might have both clinical and epidemiological implications.