Bone quantitative ultrasound generated speed of sound (SOS) is a marker of bone strength. However, critical evaluation of its validity for use in small bones is extremely limited, and SOS data may not be consistent with data obtained from dual energy × ray absorptiometry, another marker of bone strength. We report the SOS values pre and postinjection of s.c. fat using a chicken bone model; and in large for gestation and appropriate for gestation neonates to determine the influence of s.c. fat. Average SOS were lowered for the chicken bones postfat injection by 36 m/s (CS probe) and 58 m/s (CR probe), and in large for gestation group by 75 m/s (CS probe) and 51 m/s (CR probe) (p = 0.03-0.004 paired t test) although SOS measurements from each probe are significantly correlated within the large (r = 0.78) and appropriate (r = 0.83) for gestation group. Failed SOS measurements occurred significantly more frequently in the postinjection studies regardless of the probe used in the chicken bone model and for the CS probe in large for gestation neonates. The lowered bone quantitative ultrasound measurements in large for gestation neonates is likely a measurement artifact from increased s.c. fat.