A 25 years married women having one child delivered vaginaly presented in the department of Obs & Gynae, Bangabandhu Sheikh Mujib Medical University, Bangladesh on April 2013 with pelvic pain and discomfort. No history of previous pelvic trauma was present. Patient examination showed a isolated mass in the right lower abdomen, right adnexa, extending to the pelvic wall upto lower end of ureter. Tumor markers were within normal limit. Intravenous pyelogram (IVP) showed mild right hydroureter and hydronephrosis with obstruction at the lower end of ureter. She was diagnosed as a case of adnexal mass with mild hydroureter & mild hydronephrosis and it was decided to operate on the patient. The surgical approach was transabdominal. On laparotomy a pseudocystic lesion 12×10cm in size was found over the right paracolic gutter and extending down into the pelvis involving the right parametrium. No abnormality was found in the uterus or tubes. The histological examination revealed a desmoid tumor of the pelvis. The patient's recovery was uneventful.