The loss of one allele for glial cell line–derived neurotrophic factor (GDNF) results in ≈30% fewer but normal sized glomeruli in young mice. Low nephron number, inherited or acquired, has been linked to increased risk of development of hypertension and renal failure. This study examines whether GDNF heterozygous mice, with an inherent reduction in nephron number, demonstrate a deterioration in renal structure and function and rise in arterial pressure in later life. Fourteen-month-old male GDNF heterozygous (n=7) and wild-type (n=6) mice were anesthetized and prepared for measurement of mean arterial pressure, glomerular filtration rate (GFR), and renal blood flow. After measurement of renal function, kidneys were fixed for stereological determination of total glomerular number and mean glomerular volume. Mean arterial pressure was, on average, 18 mm Hg higher in GDNF heterozygous (98±4 mm Hg) than wild-type mice (80±2 mm Hg; P<0.01). However, GFR (0.656±0.054 versus 0.688±0.076 mL/min per g kidney wt) and renal blood flow (5.29±0.42 versus 4.70±0.34 mL/min per g kidney wt) were not different between groups. Fourteen-month-old GDNF heterozygous mice had ≈30% fewer glomeruli than wild-type mice (9206±934 versus 13440±1275; P<0.01) and significantly larger glomeruli (4.51±0.39 versus 3.72±0.63×10⁻⁴mm³; P<0.01). Thus, aged GDNF heterozygous mice maintained a normal GFR and renal blood flow despite reduced nephron numbers. The elevated arterial pressure, glomerular hypertrophy, and hyperfiltration demonstrated in the GDNF heterozygous mice at this age may indicate a compensatory mechanism whereby GFR is maintained in the presence of a reduced nephron endowment.