The simultaneous acquisition method in SPECT has some advantages, such as potentially doubling throughput in an examination and halving the acquisition time. However, interradionuclide scattering limits diagnostic accuracy. We evaluated99mTc and201Tl scattering using three energy windows. These windows were set at 71 keV with 15% window width for201Tl images, at 90 keV with 10% window width for scatter images, and at 140 keV with 15% window width for99mTc images. From phantom studies, the scatter correction coefficient, a, was measured to be 1.07, while the crosstalk correction coefficient, β, was measured to be 0.14. The corrected counts, a, in the 71 keV window for201Tl image and the corrected counts, b, in the 140 keV window for99mTc image were given as follows : a =A-αC, b =B-βa, where A is the raw counts in the 71 keV window, B the raw counts in the 140 keV window, and C the raw counts in the 90 keV window. Simultaneous dual-radionuclide99mTc/201Tl scintigraphy is feasible using99mTc scatter and201Tl crosstalk correction coefficients.