We reviewed 3226 consecutive core biopsies (CBs) of 3054 mammographically detected breast lesions performed at our Centre from November 1993 to June 2003. CB diagnoses, classified according to the Non-operative Diagnosis Subgroup of the British National Health Service Breast Cancer Screening Programme (NHSBSP), were B5 (37.1%), B4 (0.5%), B3 (7.6%), B2 (50.9%) and B1 (3.9%). It was necessary to repeat the procedure in 172 cases (5.3%). The values for absolute sensitivity and specificity are 90.8% and 83.8%, respectively. The positive predictive value for categories B4 and B5 is 100%, with no false-positives. The positive predictive value for category B3 is 16.3%. The negative predictive value for B2 category is 97.2%, with a false-negative rate of 3.5%. In conclusion, this system of analysis has enabled us to confirm that our CB results surpass the minimum recommended standards proposed by the NHSBSP.