Aims and background Microinvasive biopsy techniques are increasingly employed in the diagnostic assessment of non-palpable breast lesions (NPBLs). This study reports the four-year experience of an Italian surgical center in the evaluation of the diagnostic effectiveness versus adverse effects of vacuum-assisted core biopsy (Mammotome). Methods 314 NPBLs with a dubious ultrasound and/or radiographic appearance were subjected to mammography-guided (86) or ultrasound-guided (228) Mammotome biopsy. Results The procedure could be completed and was diagnostic in 305 cases (P <0.0001). Adverse events were transient lightheadedness. in two cases and moderate bleeding in three cases. Histological processing of the biopsies showed 227 cases of benign disease (74.42%), 68 cases of carcinoma (20 carcinomas in situ and 48 infiltrating carcinomas) (22.29%), nine cases of atypical ductal hyperplasia (2.95%) and one atypical lobular hyperplasia (0.33%). Only 12 patients reported mild discomfort relative to the procedure. The difference between the number of patients reporting discomfort and that of patients reporting no discomfort at all was highly significant (P <0.0001). Conclusions The results confirm that Mammotome biopsy is a highly effective procedure for the diagnosis of NPBLs, with minimal negative effects.