Low birth weight predisposes to renal disease in Aboriginal adults. This could be due to reduced nephron numbers, which might be reflected in lower kidney volumes, at least early in life. In this study we evaluated the association of birth weight with renal volume in 174 children and in adolescents 5 to 18 years old in an Aboriginal community with high rates of renal disease. Their mean birth weight was 2.9 kg, and 19% had been low birth weight (<2.5 kg). Kidney dimensions were measured by ultrasound by a single observer, and kidney volume (KV) was calculated from the formula KV (mL) = length x (depth 1 + depth 2)/2 x 0.523. Combined kidney volume, corrected for body surface area (corrKV), was independent of age and averaged 240 +/- 45 mL/1.73 m(2). The average corrKV was significantly lower (by about 20 mL) in low birth weight children than in those with "normal" birth weight. There was a difference of 32 mL in combined corrKV between children in the lowest versus the highest quintile of birth weight. Disparities in calculated kidney volume were driven more by lower kidney depth than length in low birth weight children. We conclude that low birth weight children have lower renal volumes than children of higher birth weights, after correction for current body size. This conclusion is compatible with the theory that intrauterine growth retardation is associated with reduced nephron endowment. The susceptibility to renal disease associated with low birth weight in this population might be mediated in part through this mechanism.