Cloacal dysgenesis is frequently associated with uterine anomalies. We report a case of pregnancy which resulted in an abortion in a woman with a persistent cloaca. Presumptive diagnosis before operation was ectopic pregnancy of the left tube. Postoperatively, the site of implantation of the conceptus was found to be the cavity of a unicornuate uterus in association with a rudimentary horn, the presence of which misled us to diagnose an ectopic pregnancy.