The use of fructose as a pure sugar has considerably increased in the last 3 decades, especially as a sweetener in carbonated beverages. Our previous studies showed that long-term fructose intake adversely affected several age-related metabolic parameters. The purpose of the present study was to compare the consequences of long-term fructose intake with those of glucose or sucrose on renal morphology and on several biochemical parameters used to estimate renal function. Male rats were fed a commercial diet for 16 months, and had free access either to water (control) or to 250 g/L solutions of fructose, glucose, or sucrose. Fructose-drinking rats exhibited higher liver weights compare to the other dietary groups. Control rats excreted significantly less urinary output than all sugar groups, which did not differ from each other. No differences were observed in fasting plasma fructose, glucose, and creatinine levels, or in urinary glucose levels. Fructose consumption resulted in elevated urinary fructose levels, higher creatinine clearance, and marked proteinuria. The tested sugars had influence on the molecular weight distribution of urinary proteins in the ranges of 10 to 16, 25 to 35, and 75 to 85 kd. Histological examination revealed that fructose consumption led to the formation of foci of cortical tubular necrosis with chronic inflammatory infiltrate, accumulation of tubular hyaline casts, thickening of the Bowman's capsule, mesangial thickening due to collagen deposits, and the occurrence of hemosiderin in tubular cells. These data suggest that fructose has a negative impact on kidney function and morphology. Further research is required to elucidate the precise mechanisms by which long-term fructose consumption hampers renal metabolism.