Abstract--The importance of nephron endowment and salt intake for the development of hypertension is under debate. The present study was designed to investigate whether reduced nephron number, after completion of nephrogenesis, or chronic salt loading causes renal injury and salt-sensitive hypertension in adulthood. Rats were operated at 3 weeks of age (after completed nephrogenesis) and then subjected to either normal or high-salt diets for 6 to 8 weeks. Four different experimental groups were used: sham-operated animals raised with normal-salt diet (controls) or high-salt diet (HS) and uninephrectomized animals raised with normal-salt diet (UNX) or high-salt diet (UNX+HS). In the adult animals, renal and cardiovascular functions were evaluated and blood pressure recorded telemetrically under different sodium conditions (normal, high, and low). Hypertension was present in UNX+HS (122±9 mm Hg), UNX (101±3 mm Hg), and HS (96±1 mm Hg) groups on normal-salt diets compared with the controls (84±2 mm Hg), and the blood pressure was salt sensitive (high- versus normal-salt diet; 23±3, 9±2, 7±2, and 1±1 mm Hg, respectively). The hypertensive groups (UNX+HS, UNX, and HS) had increased diuresis and reduced ability to concentrate urine. The glomerular filtration rate (milliliters per minute) in anesthetized rats was reduced in the UNX+HS (2.36±0.30) and UNX animals (2.00±0.31) compared with both HS animals (3.55±0.45) and controls (3.01±0.35). Hypertensive groups displayed reduced plasma renin concentrations during high sodium conditions and hypertrophic kidneys and hearts with various degrees of histopathologic changes. In conclusion, at a young age after completed nephrogenesis, uninephrectomy or chronic salt loading causes renal and cardiovascular injury with salt-sensitive hypertension.