Background: Lactating adenoma is a rare benign breast tumor that occurs during pregnancy or breastfeeding. Excessive bleeding from such lesion during biopsy has been previously reported in several cases. This is the first report of excessive spontaneous bleeding from a lactating adenoma triggered by the onset of labor. Case Presentation: We report of a case of a 33 years old African woman pregnant at 38 weeks who presented to us complaining of a rapid enlargement of her right breast for 8 months with a prior history of a diagnosis of an ipsilateral breast fibroadenoma. Physical examination revealed a 15*15cm right breast swelling with a 3*4cm ulcer on the right lower inner quadrant which had indurated margins and a shallow floor, no palpable lymph nodes. Excessive spontaneous intractable bleeding occurred from the mass during labor to necessitate an emergency mastectomy. Histological analysis of the mass confirmed a lactating adenoma. Conclusion: Lactating adenomas often run a silent clinical course. Redistribution of blood volume in the breast blood vessels during labor and delivery coupled with tissue necrosis by the tumor can results in excessive spontaneous loss of blood from the affected breast to necessitate emergency mastectomy.