Abnormal fusion of mullerian duct or insufficient absorption of the uterine septum results in the anatomical abnormalities in the female genital system. The frequency of congenital uterine anamalies varies in fertile female population between 1/200 to 1/600. Unicornuate uterus with rudimentary horn is a very rare anamoly with a frequency of 1/100,000. These patients present with various gynaecological and obstetrical complications like dysmenorrhea, dyspareunia, chronic pelvic pain and rarely with acute abdominal symptoms following distension and torsion of the rudimentary horn. Obstetrical complications seen include abortions, ectopic pregnancy, preterm labour and rupture of rudimentary horn. The ultrasound, MRI and laparoscopy along with hysteroscopy are the important tools in diagnosing this rare anamoly.We are presenting a case of 16 year old unmarried girl who presented to us with severe progressive dysmenorrhea since menarche. Patient was initially diagnosed as bicornuate uterus on ultrasonography. However MRI confirmed the presence of unicornuate uterus with rudimentary horn we performed diagnostic/operative laparoscopy along with hysteroscopy followed by excision of the rudimentary horn.