The impact of soft tissue in vivo on accuracy of bone mineral density (BMD) measurements of the spine and hip by dual energy X-ray absorptiometry and of the forearm by single photon absorptiometry was assessed by use of 14 human cadavers. The in vivo accuracy errors (SEE%) were: forearm 3–5%, anteroposterior spine 5.3%, lateral spine 10–12%, and femoral greater trochanter, neck, total, intertrochanteric, and Ward's triangle 3%, 6.5%, 6.7%, 8%, and 11–13%, respectively. Except from the lateral spine and the greater trochanter, the slopes of the linear regressions of in vivo BMD against in vitro BMD were not significantly different from 1 (p > 0.05). The calculated random accuracy error of BMD measurements due to fat inhomogeneity was estimated to 3–4% for the anteroposterior spine and 9–14% for the lateral spine (from abdominal computed tomography in 26 healthy women). In conclusion, acceptable accuracy errors below 6–7% (of soft tissue in vivo) of BMD measurements were obtained in the anteroposterior spine, the forearm, and the neck, greater trochanter, and total proximal femur.