Diabetic mastopathy is an uncommon disorder of the breast seen mostly in young women suffering from type 1 diabetes mellitus. The presenting symptom is a rapidly growing breast lump that may simulate breast cancer. Clinically and radiologically it can be indistinguishable from breast carcinoma. Recognizing this clinical entity, in addition to close collaboration between the clinician and the pathologist can facilitate its early diagnosis, avoiding unnecessary alarm for the patient. A 36 years old patient with a long-standing type 1 diabetes mellitus was admitted to surgery for a rapidly growing left breast lump. Excisional biopsy of the lump revealed diabetic mastopathy.