Purpose The mortality rate of peritoneal dialysis (PD)patients is still high, and the predicting factors for PD patient mortality remain to be determined.This study aimed to explore the relationship between the standard deviation (SD) of extracellular water/intracellular water (E/I) and all-cause mortality and technique failure in continuous ambulatory PD (CAPD) patients.Methods All 152 patients came from the PD Center between January 1 st 2006 and December 31 st 2007.Clinical data and at least five-visit E/I ratio defined by bioelectrical impedance analysis were collected.The patients were followed up till December 31st 2010.The primary outcomes were death from any cause and technique failure.Kaplan-Meier analysis and Cox proportional hazards models were used to identify risk factors for mortality and technique failure in CAPD patients.Results All patients were followed up for 59.6 ± 23.0 months.The patients were divided into two groups according to their SD of E/I values: lower SD of E/I group (≤0.126) and higher SD of E/I group (>0.126).The patients with higher SD of E/I showed a higher all-cause mortality (log-rank x2 =10.719, P =0.001)and technique failure (log-rank x2 =9.724, P =0.002)than those with lower SD of E/I.Cox regression analysis found that SD of E/I independently predicted all-cause mortality (HR 3.551, 95 % CI 1.442-8.746, P =0.006)and technique failure (HR 2.487, 95 % CI 1.093-5.659,P =0.030) in CAPD patients after adjustment for confounders except when sensitive C-reactive protein was added into the model.Conclusion The SD of E/I was a strong independent predictor of all-cause mortality and technique failure in CAPD patients.