We performed a retrospective chart review of 32 patients on peritoneal dialysis (PD) for longer than 5 months (range 5-64 months) in an attempt to identify risk factors influencing the preservation of renal function. Residual renal function (RRF) was evaluated by measurement of creatinine clearance (Ccr) from 24-hour urine collections. Risk factors examined included age and Ccr at start of PD, presence of diabetes, mean arterial pressure (MAP), diastolic blood pressure (DBP), and peritonitis rate. Multiple regression analysis was performed to determine the correlation of these factors to the rate of decline of Ccr. Loss of RRF in all patients was 0.3 mL/min/month (median 0.2, range 0.04-1.7). The contribution of RRF to total Ccr was 39% (range 12%-72.5%). Patient age, presence of diabetes, MAP, DBP, peritonitis rate, and Ccr at the start of PD had no influence on the rate of RRF loss. Nine patients in the study (28%) had been on PD longer than 2 years and still had significant renal function (mean Ccr 3.3 mL/min), which was 40% of their total weekly Ccr. These results show that PD patients can maintain RRF for extended periods and that RRF contributes substantially to their weekly Ccr. The risk factors evaluated did not influence the rate of renal function loss.