Most of the adolescent girls complain of pain during periods. The incidence of dysmenorrhea is 25%. A 17 year old girl came with right sided pain which was mistaken for appendicitis and had laparoscopic appendicectomy. She was referred to gynecology outpatient department since the pain on the right side was not relieved even on medical treatment. Repeatedly she took leave from her school. At one stage patient was thought to be malingering and was referred for psychotherapy. MRI showed class IV bicornuate unicollis uterus, with partially underdeveloped rudimentary horn with functional endometrium. The provisional diagnosis prior to laparotomy was bicornuate uterus but on surgery it was found to be a unicornuate uterus with non-communicating rudimentary horn on the right side with functioning Endometrium. There was no associated renal abnormality and endometriosis. The functioning unicornuate horn was attached to the uterus by a fibrous band which was excised easily. The patient was relieved of dysmenorrhea. In unilateral dysmenorrhea the probability of congenital malformation should be thought of. Early diagnosis and management will help to prevent a lot of complications like endometriosis, infertility, ectopic pregnancy and rupture of underdeveloped pregnant horn.CASE REPORT: A17 year old girl was referred from surgical department who had laparoscopic appendicectomy for right sided lower abdominal pain. She had severe dysmenorrhea for the past 3 years. The pain was typically felt over the right lower abdomen and it started just before the menstrual cycle, reached its peak on the third day of the menstrual cycle. She also gave a history of taking analgesics on and off for it. On examination, her vitals were stable and no abnormality was detected, everything was normal except for the tenderness at the right iliac fossa. She was advised ultrasonography (USG) to rule out any pelvic pathology. USG showed bicornus unicollis rudimentary horn 35 x 31mm with endometrium. (Figure 1) To confirm the diagnosis, magnetic resonance imaging (MRI) was performed showing class -IV bicornuate unicollis uterus, relatively small sized or partially underdeveloped rudimentary horn with functional endometrium and right hematometra. (Figure 2) Intravenous pyelography showed no renal pathology. Even though laparoscopy is preferred we did laparotomy.