This 20th Annual Data Report reports data through 2006. This year we present a new volume on chronic kidney disease (CKD) in the United States, estimating the population using National Health and Nutrition Examination Surveys. We also use diagnostic codes and laboratory data to estimate the population within employer group health plans, assess use of the new International Classification of Diseases, Ninth Revision, Clinical Modification CKD diagnosis codes, and report on morbidity, mortality, care during the transition to end-stage renal disease, and expenditures in patients with CKD. In 2006, a total of 110,854 patients started end-stage renal disease therapy, with the prevalent population reaching 506,256; a total of 18,052 transplantations were performed; and 151,502 patients had functioning grafts at year end. Program expenditures reached $33.5 billion, with $22.7 billion from Medicare accounting for 6.4% of total Medicare expenditures. The incident rate increased 3.4% to 360 per million-the highest in 5 years. Treatment targets are now reached by 93% of hemodialysis patients. Fistula use is 45.4% in prevalent patients, with attempted placements doubling since 1996. Catheter use continues to be a concern. Hemoglobin levels greater than 12 g/dL are common, particularly in some providers. First year mortality rates for incident hemodialysis patients have decreased for the first time in 11 years; however, pediatric patient survival has not improved. The rate of infectious hospitalizations in the first year of dialysis therapy now equals that of cardiovascular hospitalizations. The public health impact of kidney disease is larger than previously appreciated, and early detection, education, intervention, and risk-factor control are needed to address the heavy burden of cardiovascular disease and adverse events in this vulnerable population.