A lactating woman in her early 40s with a strong family history of breast cancer presented with a markedly swollen breast days after having a vacuum-assisted core biopsy performed to sample indeterminate microcalcifications in her left breast. Ultrasound showed a large peri-implant fluid collection which yielded milky fluid on aspiration consistent with galactocele formation. Histology of the core specimens revealed a fragment of fibrous capsule suggesting that the core biopsy had created a fistula between the breast tissue and the peri-implant space. Bromocriptine was given and the galactocele slowly resolved. Copyright 2013 BMJ Publishing Group. All rights reserved.