BACKGROUND Mammary hamartoma is a benign rare tumour occurring in both sexes, with size range mostly between 2-4 cm. Giant breast hamartoma (GMH) is very rare and can reach unexpected sizes in women. METHODS A 26 year old Egyptian female presented with left breast lump since 3 years, gradually increasing in size, with no other associated complaints. No family history of breast cancer, she did not smoke or consume alcohol, and had no past medical history. Examination revealed a large soft freely mobile mass (12 × 9 cm) in the lower outer quadrant of the left breast at the 3-6 o'clock position. There were no palpable axillary lymph nodes in both sides. Nipples and right breast were normal. CONCLUSIONS The diagnosis of GMH can be made by examination and imaging only. The specific features that appear in mammogram and ultrasound can be used to reduce the need for core biopsy in hamartoma. Wide local excision is curative. We include a review of the literature of cases of GMH > 10 cm published during the last 15 years. CONCLUSIONS A non-invasive mammogram and ultrasound provide sufficient evidence of the tumour, hence core biopsy might not be critically required. However, if a breast hamartoma is still clinically suspected but with inconclusive or unequivocal mammographic and ultrasonographic features or if there is suspicion of dysplasia, then invasive core biopsy is justified. Recurrence is low and prognosis is good.