The objective of this study was to assess bone strength using quantitative ultrasound (QUS, Sunlight Omnisense) in pre- and early-pubertal normal weight (NW, % body fat < or = 20, n = 28), and overweight (OW, % body fat < or = 25, n = 15) boys. Groups were similar in chronological and skeletal age, sexual maturity, sports participation, and calcium intake. Leisure-time physical activity was lower in OW boys. Radial speed of sound (SOS) was similar in the two groups. Tibial SOS, however, was significantly lower in OW compared with NW (3,554 +/- 109 vs. 3,646 +/- 71 m.s-1, respectively). Among pre- and early- pubertal boys, higher adiposity appears to be associated with lower bone SOS in the lower extremities.