Background: The aim of the present study was to evaluate the clinical relevance of the edema index in incident peritoneal dialysis (PD) patients. Patients and Methods: We identified all adults who underwent PD. The edema index was defined as the ratio of extracellular fluid to total body fluid. Participants were divided into two groups according to the cutoff value of their baseline edemaindex: High (＞cutoff value) and Low (≤cutoff value). Survivors during the first year after PD initiation were divided into two groups according to the initial and 1-year edema index: Non-improvement (maintenance of criteria in the initial Low group duringthe year) and Other (all participants except the those in the Non-improvement group). Results: In total, 631 patients were enrolled in the present study. The cutoff value of the edema index for 1 year mortality was ＞0.371 in men and ＞0.372 in women. The respective mean initial residual renal function (RRF, mL·min-1·1.73 m-2) in the Low and High groups were 4.88 ± 4.09 and 4.21 ± 3.28 in men, and 3.19 ± 2.57 and 2.98 ±2.70 in women (men: p＝0.108; women: p＝0.531). There were no significant differences between groups in either sex. The respective mean RRF at 1 year after PD initiation in the Low and High groups were 3.56 ± 4.35 and 2.73 ± 2.53 in men, and 2.80 ± 2.36 and 1.85 ± 1.51 in women. RRF at 1 year after PD initiation was higher in the Low group than in the High group (men: p＝0.027; women: p＝0.001). In men, the cumulative 5-year survival rates were 78.7% and 46.2% in the Low and High groups, respectively. In women, those were 77.2% and 58.8% in the Low and High groups, respectively. For survivors during the first year after PD initiation, the Non-improvement group was associated with a poor survival rate compared with the Other group in both sexes. Conclusions: A high edema index was associated with mortality in incident PD patients at baseline and follow-up. This study demonstrated that the edema index is a new marker and parameter for predicting mortality in PD patients.