Outcomes among dialysis patients vary considerably internationally and across regions within the United States. The Dialysis Outcomes and Practice Patterns Study (DOPPS) is a large, prospective, observational study of representative samples of hemodialysis patients in France, Germany, Italy, Japan, Spain, the United Kingdom, and the United States. The DOPPS collects a wealth of data regarding the patients' demographic characteristics, medical histories, laboratory values, prescriptions, dialysis unit practices, and outcomes. The study seeks to clarify which dialysis practices contribute to improved mortality rates, hospitalization rates, health related quality of life, and vascular access outcomes, after adjusting for the effects of comorbid disease and demographic variables. Over 18,000 patients have been enrolled to date. This paper describes the initial findings and outlines the plans to expand the trial.