Massive unilateral virginal breast hypertrophy in a 13-year-old girl was treated by right breast reduction, with removal of 2,968 g of breast tissue. A year later, the patient had enlargement of the left breast, and contralateral reduction mammoplasty was done. Two-year follow-up has shown no further enlargement. This case lends itself to a discussion with regard to the differential diagnosis of unilateral breast hypertrophy in adolescence. True virginal gigantomastia is relatively rare. Surgical reduction mammoplasty plays a pivotal role in the treatment of massive virginal breast hypertrophy.