Our study was aimed at investigating the efficacy of scintigraphy with 99mTc-Sestamibi (MIBI) as a support to mammography and US in the diagnosis and staging of breast cancer. Twenty-seven women with breast lesions were examined: the masses, detected at mammography and US, ranged in diameter 0.7 to 2.5 cm; mass features suggested a benign lesion in 5 patients, a malignant lesion in 9 patients and a questionable diagnosis in 13 patients. 99mTc-MIBI scintigraphic images were analyzed blind by two observers and the pattern was considered positive when tracer uptake was demonstrated at the lesion. In neoplastic lesions, tracer uptake was looked for also in the axilla. All the patients were submitted to surgery and, in case of malignancy, lymphadenectomy was also performed. MIBI scintigraphy was negative in 14/16 benign lesions and positive in 9/11 malignant lesions. Tracer uptake in the axilla was observed in 3 of 5 patients with nodal involvement. Scintigraphy had 82% sensitivity, 87% specificity and 85% accuracy in the diagnosis of breast cancers.