BACKGROUND:Peritoneal dialysis (PD) provides outcomes similar to hemodialysis, but its use has decreased in the United States despite its potential for substantial taxpayer savings. We undertook this study to determine the relationship between dialysis unit ownership with PD use and outcomes. STUDY DESIGN:Observational study. SETTING & PARTICIPANTS:All incident dialysis patients (1996 to 2004) from the US Renal Data System. PREDICTOR:Large dialysis organization (LDO), defined as corporations owning 20 or more freestanding dialysis units located in more than 1 state. OUTCOMES & MEASUREMENTS:Odds for an incident dialysis patient undergoing PD and hazards for death on follow-up in incident PD patients for each of the 5 LDOs (non-LDO as reference). RESULTS:During the 9-year period, 785,531 patients started maintenance dialysis therapy; the proportion receiving care in LDOs increased from 39% to 63%. There were consistent differences in PD use. It was significantly lower in LDO 2 (adjusted odds ratio [OR], 0.66; 95% confidence interval [CI], 0.64 to 0.68), LDO 3 (OR, 0.82; 95% CI, 0.80 to 0.85), and LDO 4 (OR, 0.96; 95% CI, 0.92 to 0.995) and higher in LDO 1 (adjusted OR, 1.06; 95% CI, 1.02 to 1.11) and LDO 5 (adjusted OR, 1.09; 95% CI, 1.06 to 1.12). Between 2000 and 2004, LDO 2 had the least use and greatest risk of death (hazard ratio, 1.08; 95% CI, 1.02 to 1.14); LDO 1 had greater use and the lowest death risk (hazard ratio, 0.87; 95% CI, 0.78 to 0.96). LIMITATIONS:Only cross-sectional associations can be described. CONCLUSIONS:Three of the 5 LDOs had consistently lower PD use. Patients treated in the LDO with the lowest use of PD had the greatest risk of death. Understanding relationships among providers, physicians, and dialysis modality use may help devise strategies for increasing PD use in appropriate patients. This has the potential to reduce the cost of renal replacement therapy and further improve outcomes.