Abstract: The purpose of this study was to determine whether there is a criterion that can be utilized to determine if excisional biopsy is indicated following the diagnosis of lobular neoplasia (LN) on core biopsy. Retrospective review of patient records with diagnosis of LN as highest risk diagnosis on core biopsy was performed. LN was defined to include both atypical lobular hyperplasia (ALH) and lobular carcinoma in situ (LCIS) and was categorized as focal or diffuse. The pathology was correlated with the mammographic finding to determine whether the diagnosis of LN was incidental or related to the mammographic finding. For those patients who did not undergo excision, follow-up data are presented along with treatment information. A total of 4,555 breast core biopsies were performed at our institution from January 1997 through March 2005. Of these, 35 patients were diagnosed with LN. Twenty six (74%) went on to excision and nine (26%) were followed. Biopsy was recommended for mammographically detected calcifications in the majority of cases. Twenty four (92%) of the 26 excised cases had focal LN and 2 of 26 (8%) had diffuse LN. Infiltrating lobular carcinoma was diagnosed in both cases of diffuse LN and no infiltrating carcinoma was seen when focal LN was diagnosed on core. Excision may not be necessary when a diagnosis of only focal LN is made on core biopsy. Diffuse LN may indicate an associated invasive cancer and should prompt excision.