Overview Objective: To present unusual case of rapidly growing breast fibroadenoma during pregnancy. Case report: Breast fibroadenomas are hormone-dependent tumors which can grow rapidly during pregnancy. We present a case of giant fibroadenoma, first detected before pregnancy, which grew rapidly under the influence of pregnancy hormones and was excised in the third trimester. Conclusion: Fibroadenomas are benign breast lesions in young women. They are hormone-dependent tumors, which can grow rapidly especially during pregnancy and/ or lactation and imitate malignancy. In each case of a newly created breast lesion, it is necessary to proceed responsibly to the clinical examination, which is a base for further decision concerning the necessity of taking a bio­psy for histological verification. Keywords: breast fibroadenoma – pregnancy – lactation – phyllodes tumor