The efficacy of Tc-99m sestamibi scintimammography in the detection of breast carcinoma has been proven in previous studies. In this study we evaluated the influence of active mammary inflammation on Tc-99m sestamibi scintimammography and its ability to detect breast malignancy in the presence of this condition. Twenty-one women with acute nonpuerperal mastitis underwent breast scintimammography using Tc-99m sestamibi. Their mean age was 49.6 years. In 15 women the scan was positive, 2 suffered from inflammatory carcinoma of the breast, and all the other women had acute mastitis. Six patients had a negative scan, and in all of them, acute mastitis was diagnosed. Total accuracy, sensitivity and specificity in the detection of breast mastitis were 62%, 68%, and 88%, respectively. Scintimammography in patients with acute inflammation of the breast is frequently positive in the absence of malignant condition, therefore it should not be used during acute mastitis for the detection of breast cancer.