Spontaneous perforation of the uterus is rare and only several cases have been reported in the English medical literature. Most of the patients had gynecological malignancy and almost all were associated with cervical occlusion. We report a case of diffuse peritonitis resulting from spontaneously perforated pyometra with an intrauterine device (IUD) inserted for more than two decades. This case differs from others in that the cervical canal was not occluded. In the absence of other possible causes of uterine perforation, the etiology in this case is mostly likely hemorrhagic necrosis related to the long-term IUD.