This study is part of a five-year project to investigate the long term effect of chronic hemodialysis on patients with end-stage renal failure. Previous research has associated hemodialysis with progressive dialysis encephalopathy (PDE), which is characterized by speech disturbances, cognitive impairment, myoclonus and behavioral changes. Little is known about the cause or the course of this syndrome except that it begins 14-36 months after treatment onset and usually culminates in death. The purpose of this study was to investigate neuropsychological (cognitive and behavioral) functioning in dialysis patients over a period of years. To date, 34 patients have been studied for 22 months utilizing a cross-sectional method comparing patients at different stages of treatment combined with a longitudinal method of repeated evaluations over time. Current findings show improved cognitive functioning during at least the first year of treatment and no evidence of cognitive deterioration in patients on dialysis for more than one year (M = 4.3). These findings offer strong evidence that PDE is not necessarily a general phenomenon among patients on chronic hemodialysis.