Core needle biopsy (CNB) is increasingly being used in the investigation of breast disease whether this is asymptomatic and suspected after screening mammography, or presents symptomatically in the patient. In most cases, the result of the procedure provides a definitive diagnosis or at least provides information that is used to plan the further management of the patient. There are, however, a number of unresolved issues with the use of CNB; for example, with regard to the amount of information that can be reliably derived from CNB or with regard to the management of the patient after some CNB diagnoses. Oestrogen and progesterone receptors and HER2 are reported on both core biopsies and excision specimens, but there continues to be debate over which represents the more appropriate specimen type on which to perform these tests. There are a number of possible diagnoses after CNB for which the management is not straightforward and around which there may be controversy, or just a lack of sufficient evidence to support a definite management plan. These 'lesions of uncertain malignant potential' include papillary lesions, fibroepithelial lesions with cellular stroma, mucocoele-like lesions and radial scars. Currently, these are removed surgically but there may be an argument for more conservative management including vacuum-assisted core excision in some cases.