Objective: To evaluate the prevalence of chronic kidney disease (CKD) in hospitalized patients and determine the proportion of these patients with/without a diagnosis of CKD based on estimated glomerular filtration rates (eGFR). Methods: A retrospective analysis of US hospital data in the Cerner Health Facts® database during January 2000 and March 2007 was conducted. Inclusion criteria were age 18 years, a SCr measurement 3-18 months before hospital admission and seven days before or three days after hospital admission. Patients who had dialysis, acute renal failure and/or mixed inpatient eGFR (some values <60 and others =60 mL/min/1.73m2) were excluded. To minimize bias and misclassification due to hospitalization circumstances, 2 eGFR values <60 mL/min/1.73m2 were used to designate patients with CKD. The first eGFR was determined from the closest SCr measurement within 3-18 months before hospitalization and the second eGFR was determined using a SCr seven days before or three days of hospital admission. The MDRD-4 equation was used to calculate eGFR. Results: Of the 1,265,014 patients hospitalized over the seven years evaluation, 193,221 met the inclusion criteria. Approximately 21% of patients were subsequently excluded for dialysis, acute renal failure, and/or mixed eGFR (n=40,937). Overall, 27% of patients (n=41,495) had an eGFR <60 mL/min/1.73m2 at admission. Of these, 81% (n=33,443) had an eGFR <60 mL/min/1.73m2 prior to admission. Of this subset likely to have CKD based on chronically low eGFR, only 26% (n=8,560) had a diagnosis of CKD at admission based on ICD-9-CM diagnosis. Conclusion: Our findings suggest that most patients with RKF upon hospital admission may have CKD. Of these, few seem to have supportive CKD diagnosis codes. Identification and diagnosis of this patient population during hospitalization may provide a unique opportunity to improve disease management during the inpatient stay or after discharge, and may result in earlier nephrology referrals if appropriate.