PURPOSE: To describe the changes in diagnostic methods and reassess the role of core biopsy compared with needle localization biopsy (NLB) in the evaluation of non-palpable breast lesions. MATERIALS AND METHODS: We retrospectively analyzed 930 non-palpable breast lesions which underwent either core biopsy or NLB between January 1996 and December 2000. NLB involved 511 lesions in 482 patients, and core biopsy, 419 lesions in 365 patients. For a given lesion, NLB was guided by either mammography (n=213) or ultrasonography (US) (n=298), but only US was used to guide a core biopsy. Over the five-year period, we calculated the total number of biopsies per year relating to non-palpable breast lesions, also determining the mammographic findings in cases involving NLB and the percentage of malignancies seen at histopathology. RESULTS: The total number of biopsies increased with time: 1996: n=91, 1997: n=118, 1998: n=144, 1999: n=245, 2000: n=332. The implementation of core biopsy, however, led to a decrease in the proportion of NLB (1996: 97.8%, 1997: 84.7%, 1998: 75.7%, 1999: 47.8%, 2000: 28.9%). Among nonpalpable lesions which underwent mammography-guided NLB, 46.5% (20/43) were a mass or density in 1996, while in 2000 the proportion was 5.7% (2/35). During this period, however, the finding of calcification without a mass increased from 48.8% in 1996 to 94.3% in 2000. The proportion of cases in which NLB demonstrated malignancy increased from 13.5% in 1996 to 49% in 2000; where US-guided NLB was used, the increase was remarkable: from 15.2% in 1996 to 65.6% in 2000. CONCLUSION: In the evaluation of non-palpable breast lesions, the appropriate use of core biopsy can decrease the need for a more invasive method such as NLB. Furthermore, because most benign lesions diagnosed by core biopsy do not also undergo NLB, the use of the latter increases the yield of malignancies.