Adnexal torsion is a relatively rare cause of lower abdominal pain in women, but in many cases it leads to a serious condition. We present a case of adnexal torsion of a mature cystic teratoma in which hemorrhagic infarction was reflected by progressive enlargement and wall thickening on successive plain abdominal radiographs. There has been no other report describing such changes of adnexal torsion on plain abdominal radiographs.