Since the first report of pregnancy in a rudimentary uterine horn in 1669 by Mauriceau and Vessal, there have been probably well 350~400 others. Unfortunately a rudimentary uterine horn is mostly discovered as a complication of pregnancy, but if symptomless and uncomplicated, it may not discovered forever. About its incidence, it is reported that it occurs at a rate of 1 per 100,000 or 150,000. When a rudimentary horn is discovered as a complication of pregnancy, it mostly accompanies so severe hemorrhage caused by uterine horn rupture that it is considered very dangerous for its high mortality rate. Though a rudimentary uterine horn is discovered accidentally by various other causes, it is desirable to do a surgical removal of a rudimentary horn as a principle of medical cure. And it is also reported that a rudimentary horn frequently accompanies an anomaly of urogenital system. We have once treated a patient with a rudimentary uterine rupture caused by pregnancy in department of Obstetrics & Gynecology, Kangnam General Hospital Public Corporation. Here we present a report on the case of pregnancy in a rudimentary uterine horn with the reference to other reports on it.