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Abstract: Previous reports of the effect of antecedent administration of radionuclide on bone mineral density (BMD) measurements have yielded inconsistent results. Ten subjects scheduled for 99mTc-methylene diphosphonate (99mTc-MDP) bone scanning and 10 scheduled for 99mTc-sestamibi cardiac scanning had BMD measured by dual X-ray absorptiometry (DXA) (GE/Lunar) before and within 5 hours of diagnostic radionuclide injection. Paired t test and Wilcoxon-signed rank tests were used to compare the measured differences in BMD at multiple skeletal sites. Differences were subjected to multivariate analysis of demographic factors. Mean change in measured BMD following 99mTc-sestamibi administration (ΔBMD-99mTc-sestamibi) was −0.216±0.113 g/cm2 at the total body and −0.348±0.300 g/cm2 at the lumbar spine (p <0.005). Mean change in measured BMD following 99mTc-MDP administration (ΔBMD-99mTc-MDP) was −0.058±0.037 g/cm2 at the total body and −0.053±0.049 g/cm2 at the lumbar spine (p <0.05). Mean ΔBMD-99mTc-sestamibi exceeded least significant change (LSC) in all skeletal sites except the femoral trochanter. Mean ΔBMD-99mTc-MDP exceeded LSC only at the lumbar spine. The effect was correlated with 99mTc dose but not with gender, age, body mass index, baseline BMD, or time interval from injection to scan acquisition. In conclusion, BMD measured by the GE/Lunar Prodigy densitometer is corrupted by antecedent 99mTc-sestamibi and to a lesser extent by 99mTc-MDP. This effect is greater at the total body and lumbar spine than at the hip. Caution is warranted in scheduling and interpreting DXA studies when 99mTc has been recently administered. [Copyright &y& Elsevier]