The Pediatric Peritoneal Dialysis Study Consortium (PPDSC) proposes to perform a prospective, multi-center, longitudinal study to explore the association of dialysis delivery, or dose, and clinical outcomes. Delivered dialysis will be measured as a weekly total creatinine clearance and an analytical method of quantifying urea solute transport relative to its volume of distribution. The PPDSC will measure total body water in study subjects using dilution of O18 water.