In this case report a unicorn uterus was diagnosed at a caesarean delivery in a 23-year-old woman with known foetal breech presentation and suspected low foetal weight. She had had a failed attempt of cephalic version two weeks before delivery, and her baby's weight was checked regularly in third term. Unicorn uterus is associated with a higher risk of spontaneous abortions, infertility, preterm labour, foetal malpresentation, low birth weight, caesarean delivery and renal malformations. Although pregnancies in these women can be uneventful, it is advised, that women with unicorn uteri are followed closely during their pregnancies.