The authors carried out a retrospective chart review in 114 patients treated for at least two years at the Toronto Western Hospital Peritoneal Dialysis Unit and identified eight, who gained an “excessive” amount of weight equal to or greater than 10 kg of their initial weight. These patients had gained an average of 13.1 kg over the preceding two years. They are mostly males and their average age is 51 years. They are well-nourished normotenseive nondiabetics with mostly normal cardiac function. They are adequately dialyzed (per KT/V urea), have little residual renal function and typically have peritoneal membranes characterized by high average transport. According to BIA analysis, this weight gain was likely due to an increase in fat mass accompanied by a trend toward decreasing body-cell mass. This weight gain may be due to increased caloric intake secondary to dialysate glucose absorption in the setting of high average (peritoneal membrane) transport. Such excessive weight gain also may occur if these patients have polymorphism of the UCP-2 gene, which can alter metabolic rate.