This is a case of a large lactating adenoma which developed in a 26 year old primagravida during the third trimester of her pregnancy. The presentation was that of a grossly enlarged and engorged breast with breast erythema, warmth and tenderness. Radiologic and pathologic examinations were difficult because of the lactational changes in the breast and areas of infarcted tissue within the large tumor. Skin biopsies and core biopsies of the mass were performed to exclude malignancy. Surgical resection of the mass was necessary for definitive diagnosis. The pathology proved to be a lactating adenoma, which is the most prevalent breast mass in young pregnant females. The large size of this tumor, and the presentation of breast erythema and edema raised the possibility of inflammatory breast cancer. Following surgical resection and definitive diagnosis of this tumor, the patient required plastic surgical reconstruction of the breast because of redundant breast tissue. Although most lactating adenomas spontaneously involute, the diagnosis is not always straight-forward and surgical resection may be required for definitive diagnosis and exclusion of other pathologic processes.