Unicornuate uterus is a congenital anomaly resulting from a developmental disorder of one Müllerian duct. Although rare in the general population, it is more common among infertile women and those suffering from recurrent misscarriage. It is most often asymptomatic, but may present with dysmenorrhea, chronic pelvic pain, hematometra and hematosalpinx. The incidence of infertility among these women is high due to reduced uterine muscle mass, insufficient vasculature and local uterine wall defects. Pregnancy is possible in the hemi-uterus and rudimentary horn and is considered high-risk. Pregnancy in the rudimentary horn is dangerous due to possible horn rupture. Pregnancy in the hemi-uterus is high-risk due to the high frequency of miscarriages in the 1st and 2nd trimesters, complications (IUGR, IUFD, cervical insufficiency, placental abnormalities, malpresentation) and premature birth. Most pregnancies are completed by caesarean section, and it is not uncommon for the existence of the malformation to be established only then. Timely diagnosis is often lacking due to the asymptomatic nature of the malformation, the nonspecificity of the physical finding, and the inexperience of clinicians in spotting this malformation on conventional 2D ultrasound. Diagnosis is made by a combination of physical findings with ultrasound, hysterosalpingography, and MR. Surgical correction of the hemi-uterus is not possible, therefore early diagnosis is crucial, before the onset of gynecological problems, infertility or the first pregnancy. Pregnancies need to be intensively monitored as high-risk, with a “watchful waiting” approach, in order to prevent adverse outcomes.