Purpose: Ultrasonography and $^{99m}-Tc-MIBI$ scintimammography were validated as useful diagnostic tools for primary breast cancer. However, ultrasound has the problem of low specificity. We compared the diagnostic usefulness of ultrasound with $^{99m}-Tc-MIBI$ scintimammography in the diagnosis of breast cancer. Materials and Methods: This study included 174 patients who had ultrasound and $^{99m}-Tc-MIBI$ scintimammography peformed on breast masses from 1999 to 2000. The pathologic results were obtained by surgery or FNAB. Results: Among the 174 patients, malignant breast disease numbered 117 and benign breast disease numbered 57. Ultrasound revealed 88 TP, 9 FN, 8 FP, 34 TN, and 35 indeterminate cases. $^{99m}-Tc-MIBI$ scintimammography revealed 91 TP, 25 FN, 9 FP, and 48 TN. The sensitivity, specificity, positive predictive value, and negative predictive value of Ultrasound were 66.7%, 44.2%, 67.2%, and 43.6% respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of $^{99m}-Tc-MIBI$ scintimammography were 77.8%, 84.2%, 91%, and 64.9% respectively. Among the 35 indeterminate ultrasound cases, $^{99m}-Tc-MIBI$ scintimammography revealed 13 TP, 15 TN, and 7 FP Conclusion: $^{99m}-Tc-MIBI$ Scintimammography was more sensitive and specific than ultrasound for the detection of primary breast cancer and provided more useful information in cases of indeterminate ultrasound findings.