Unicornuate uterus occurs due to a complete or partial nondevelopment of one Mullerian duct; sometimes it is associated with a rudimentary horn, which can communicate or not with uterine cavity or contain functional endometrium. Pregnancy in a rudimentary horn is rare and the outcome almost always unfavorable, usually ending in rupture during the first or second trimester with significant morbidity and mortality. Despite the availability and advances on imagiologic procedures, recognition of this ectopic pregnancy is frequently made at laparotomy after abdominal pain and collapse. The authors describe a case of a primigravida with 34 weeks of gestation admitted with a preeclampsia with severity criteria. A cesarean for fetal malpresentation was done and, unexpectedly, a rudimentary horn pregnancy was found with a live newborn. In the literature, few reports of a horn pregnancy reaching the viability with a live newborn are described, enhancing the clinical importance of this case. A review of literature concerning the epidemics, clinical presentation, and appropriate management of uterine horn pregnancies is made.