OBJECTIVE: To assess the clinical efficacy and morbidity of continuous cyclic peritoneal dialysis compared with continuous ambulatory peritoneal dialysis with a Y-connector as renal replacement therapy. DESIGN: Prospective, randomized study. SETTING: University hospital. PATIENTS: All new patients with end-stage renal failure consecutively entering the dialysis program from January 1988 through July 1991 were randomly assigned to receive continuous ambulatory peritoneal dialysis with a Y-connector or continuous cyclic peritoneal dialysis and were followed prospectively. MEASUREMENTS: Patient and technique survival, dialysis adequacy, and (infectious) morbidity. RESULTS: Forty-one patients (median age, 56 years; range, 18 to 86 years) started continuous ambulatory peritoneal dialysis with a Y-connector (follow-up, 688 patient-months), and 41 patients (median age, 54 years; range 21 to 76 years) started continuous cyclic peritoneal dialysis (follow-up, 723 patient-months). The two groups showed no significant differences in adequacy of dialysis (as assessed by blood pressure control and laboratory and neurologic variables) and patient or technique survival. Renal transplant was the primary reason for discontinuing the assigned dialysis technique in both groups. The average number of hospitalizations per patient-year was 1.0 using continuous ambulatory peritoneal dialysis with a Y-connector and 0.6 per patient-year using continuous cyclic peritoneal dialysis (P = 0.02), with a mean duration of 10.8 and 9.6 days per admission, respectively (not significant). Peritonitis occurred significantly less often in those receiving continuous cyclic peritoneal dialysis (0.94 compared with 0.51 episodes per patient-year; P = 0.03). No difference in causative pathogens was observed. Exit site infection rate was 0.38 episodes per patient-year in both groups. CONCLUSION: In an unselected patient group, continuous cyclic peritoneal dialysis was accompanied by significantly lower rates of peritonitis and dialysis-related hospital admission, whereas it was as effective as continuous ambulatory peritoneal dialysis with a Y-connector for patient and technique survival.