Scintimammography with 99mTc-MIBI is a new technique which has expanded the use of nuclear medicine to a new group of patients in whom scintigraphy was not been widely used. When performed correctly, and in those patients, such as the young, where x-ray mammography is often non-diagnostic, the sensitivity of scintimammography can exceed that of x-ray mammography with a similar specificity. A combination of the two techniques in this patient group can provide sensitivities greater than 98%. The mechanism of uptake of 99mTc-MIBI in breast tissue is better understood as is the efflux of the pharmaceutical from the tumour cell. The relationship between the efflux rate of 99mTc-MIBI and the expression of the multi-drug resistance gene may help in determining important aspects of tumour function, such as the response to cytotoxic chemotherapy. More recently the role of scintimammography has been found in those patients with suspected breast cancer recurrence where methods depending on the anatomical structure of the breast, such as mammography and MRI, are of less use. Scintimammography, when correctly performed and correctly applied, is able to deliver unique information which is of use to the patient with suspected primary or recurrent breast cancer.