Background and Aim: Although the majority of patients with end stage renal failure have anemia, some have relative erythrocytosis. Patients treated with continuous ambulatory peritoneal dialysis (CAPD) having relative erythrocytosis were studied in order to determine the factors that would be responsible. Methods: Nine out of 89 CAPD patients (10%) were identified as having relative erythrocytosis. Age-, sex- and duration of disease-matched eight patients undergoing CAPD were taken as control. Beside factors of etiologies of renal failure, smoking, renal cysts, viral hepatitides, residual renal function, the adequacy of CAPD. nutritional status. hypertension., serum levels of erythropoietin, IL-1, IL-6, TNF-, and IGF-1 levels were also investigated. Results: Relative erythrocytosis occurred most often in diabetic and amyloidosis patients. None of the parameters studied were found to be significantly different between groups. During 2-year follow-up, although statistically non-significant, patients having relative erythrocytosis seemed to have higher mortality rate due to vascular complications. Conclusion: No single factor seemed to explain erythrocytosis in patients undergoing CAPD, Being diabetic or with amyloidosis may increase the risk.