Background: Red blood cell distribution width (RDW), expresses variation in size of circulating erythrocytes, is a part of complete blood cell count test. Recent studies have demonstrated an association between RDW and adverse outcomes in patients with heart failure and coronary heart disease. Also, it has been found to be predictive of all-cause mortality in community-based cohorts irrespective of hemoglobin levels. As increased RDW levels are frequently observed in patients with end-stage renal disease (ESRD), we sought to determine whether RDW value is associated with mortality in ESRD patients treated with continuous ambulatory peritoneal dialysis (CAPD). Methods: A retrospective analysis was undertaken in 197 incident CAPD patients, who started CAPD between January 2005 and December 2010 at Yonsei University Health System and maintained CAPD for more than 3 months. Patients were divided into 2 groups according to the RDW levels at 3-month, and all-cause and cardiovascular mortalities were compared between groups. Results: The mean age was 55.1 years and 115 patients (58.4%) were male. RDW at 3-month ranged from 11.3 to 16.8% (mean 13.6±1.1%), and 51 patients (25.8%) showed elevated RDW value (>14.5%). There were significant positive correlations between RDW levels and age (r=0.22, p<0.01), Charlson comorbidity index (CCI) score (r=0.27, p<0.01), left ventricular mass index (r=0.28, p<0.05), left atrial volume index (LAVI) (r=0.26, p<0.01), the ratio of early mitral inflow velocity to peak mitral annulus velocity (E/E`) (r=0.16, p<0.05) and left ventricular end diastolic dimension (r=0.271, p<0.01). In contrast, RDW values were negatively correlated with hemoglobin (r=-0.16, p<0.05) and albumin levels (r=-0.28, p<0.01). The all-cause mortality rates were significantly higher in the high RDW group (p<0.05). Cox regression analysis revealed that RDW was a significant independent predictor of all-cause mortality even after adjustment for age, gender, CCI score, hemoglobin, albumin, total cholesterol, LAVI, left ventricular ejection fraction (LVEF), and E/E`` (HR 1.20, p<0.05). Conclusion: This study demonstrates that RDW provide a meaningful prognostic value on all-cause mortality in incident CAPD patients.