OBJECTIVES: Patients with Afib have higher risk of stroke than those without Afib.  Anticoagulant therapy prevents strokes in Afib, however, Afib patients with moderate to severe renal impairment have been excluded from trials.  The objective of this study was to assess the distribution of renal function by estimated glomerular filtration rate (eGFR) in Afib patients.  METHODS: A retrospective, cohort design study was conducted using an EMR database.  The study period was January 1996 thru December 2010 [eligibility period: 1/2006 - 12/2009 for adults diagnosed with Afib (ICD9 code 427.31)].  Index Date was first Afib diagnosis during eligibility period.  The pre-index period was Jan 1996 to Index and the post-index period defined as 12 months post Index.  Serum creatinine measurement at Index was required.  Renal function categorized by NKF Guidelines for Stage of CKD and eGFR calculated using Cockcroft-Gault Equation.  Demographic and clinical characteristics were collected, baseline and follow-up renal function determined and logistic regression conducted to assess predictors of renal function decline. RESULTS: A total of 61,840 Afib patients (mean age 69.8 years; 54.2% male) identified and categorized by CKD stage (mean age; % male) at Index:  Normal – 6,572 (58.5; 73.0%); Stage 1 – 10,901 (62.8; 68.6%); Stage 2 – 20,331 (71.3; 58.6%); Stage 3 – 21,105 (74.9; 39.5%); Stage 4 – 2,579 (75.1; 31.1%); Stage 5 – 352 (71.8; 48.9%).  Post-index patients were categorized by CKD stage: Normal – 11,788; Stage 1 – 2799; Stage 2 – 17,009; Stage 3 – 18,849; Stage 4 – 2675; Stage 5 – 401 (8,319 patients with no post-index eGFR).   Male gender and increasing age and Charlson Comorbidity Index were predictors of renal function decline (>10%) as well as CHD, CKD, DM, HF, HTN and proteinuria (p<0.05).   CONCLUSIONS: Nearly 40% of Afib patients in this study exhibited moderate to severe renal impairment.