Pre-donation kidney volume and function may be crucial factors in determining graft outcomes in kidney transplant recipients. We measured living donor kidney volumes by 3D helical computed tomography scanning and glomerular filtration rate (GFR) by 125I-iothalamate clearances in 119 donors, and correlated these values with graft function and incidence of acute rejection at 2 years post-transplantation. Kidney volume strongly correlated with GFR (Pearson r= 0.71, p < 0.001). Body size and male gender were independent correlates of larger kidney volumes, and body size and age were predictors of kidney function. The effects of transplanted kidney volume on graft outcome were studied in 104 donor-recipient pairs. A transplanted kidney volume greater than 120 cc/1.73 m2 was independently associated with better estimated GFR at 2 years post-transplant when compared to recipients of lower transplanted kidney volumes (64 ± 19 vs. 48 ± 14 mL/min/1.73 m2, p < 0.001). Moreover, recipients of lower volumes had a higher incidence of acute cellular rejection (16% vs. 3.7%, p = 0.046). In conclusion, kidney volume strongly correlates with function in living kidney donors and is an independent determinant of post-transplant graft outcome. The findings suggest that (1) transplantation of larger kidneys confers an outcome advantage and (2) larger kidneys should be preferred when selecting from otherwise similar living donors.