The authors investigated the effect of silicone breast implants (SBIs) on thallium-201 myocardial perfusion scintigraphy. Twenty-nine patients with SBIs and 14 control subjects were included in the study. All of the participants underwent a resting thallium-201 myocardial perfusion study. Comparison of the thallium images between patients with SBI and control subjects was done both visually and semiquantitatively. On visual analysis, neither image distortion nor image artifact attributable to the SBIs was noted. Semiquantitative analysis revealed that in patients with SBIs, the uptake values of the anteroseptal, anterolateral, lateroanterior, and lateroinferior myocardial walls was slightly, but significantly, lower than those of control subjects: anteroseptal, 87.7 +/- 6.0% vs. 92.8 +/- 5.1%; anterolateral, 88.0 +/- 5% vs. 92.6 +/- 4.5%; lateroanterior, 87.4 +/- 5% vs. 91.4 +/- 4.7%; and lateroinferior, 86.0 +/- 6.0% vs. 91.7 +/- 7.0%. The uptake value of the remaining walls in patients with SBIs were not significantly different than the control subjects. In conclusion, SBIs did cause a significant decrease in uptake values of the myocardial walls, which should be considered during interpretation of the images.