We report a case of adenomyosis which developed from a hypoplastic uterus and leiomyoma in a patient with MRKH syndrome. A 45-year-old Malay female with primary amenorrhoea and primary infertility presented with abdominal mass and abdominal pain. She is phenotypically female, has well developed secondary sexual characteristics, and has normal female external genitalia with shallow vagina dimple. Transabdominal ultrasonography showed a homogenous adnexal mass of 10 × 8 cm, uterus sized 5 × 4 cm, and normal kidneys. A complex mass of right adnexa was demonstrated by CT scan. Exploratory laparotomy showed torsion of right adnexal mass and rudimentary uterus with fibroid but no endometrial tissue and blind end with absent cervix. The normal right ovary and tube were not visualized. The left fallopian tube and ovary were normal. It is also complicated by vaginal agenesis. Removal of right adnexal mass and rudimentary uterus was done with preservation of left ovary. The histologic diagnosis was uterine adenomyosis and leiomyoma arising from the right adnexa, possibly from the broad ligament.