Pregnancy in a rudimentary horn is very rare condition and it generally culminates in rupture, in second trimester with torrential haemorrhage. The accuracy of ultrasound in diagnosing rudimentary horn pregnancy at an advanced gestation still remains elusive. We report a case of unruptured rudimentary horn pregnancy which progressed to 38 weeks of gestation. The diagnosis was missed at 24, 30 and 38 weeks of gestation on obstetric sonogram. The diagnosis was made at laparotomy when the patient was planned for caesarean section in view of placenta accreta.