The availability of technological advances like ultrasonography (USG) and magnetic resonance imaging (MRI) has made the diagnosis of rudimentary horn pregnancy possible at an early gestation. However, in advanced pregnancy, such cases can sometimes pose a diagnostic dilemma and are recognized only when patient presents with abdominal pain and collapse and is taken for laparotomy. We report one such rare case of a nulliparous female who was carrying on well with her pregnancy till she developed symptoms of acute abdomen at 28 weeks of gestation. She underwent USG and MRI but it was only after laparotomy that a final diagnosis of a pregnancy in a rudimentary horn with placenta percreta perforating through the fundus could be made. There was a significant amount of hemoperitoneum; however, the horn was intact and the fetus could be salvaged. We excised the rudimentary horn with ipsilateral tube and ovary. Post operatively, both the mother and the baby were discharged in healthy condition.