Background Intrauterine devices (IUD) are widely used all over the world. One of the most serious complications is uterine perforation, and it is very rare for the IUD to penetrate the bladder after perforation. Here we report two cases of IUD migration into the bladder, and review the literature to analyze the possible causes and solutions of such complications. Case presentation Case NO. 1 is a 37-year-old female who presented lower urinary tract symptoms for a year. Cystoscopy showed that a strip of metal penetrated into the bladder, and the surface was covered with stones. The patient underwent cystotomy and foreign body removal under general anesthesia. Case NO. 2 is a 46-year-old woman who previously inserted an IUD in 1998, but she had an unexpected pregnancy in 1999. Her doctor believed that "the IUD had spontaneously expulsed" and a new IUD was inserted after her pregnancy was terminated. Her CT scan showed an IUD on the left side of the bladder and another IUD in the uterus. Her foreign body was removed by cystotomy. Conclusion Patients with IUD should be suggested to check the device regularly, and those who with a missed IUD have to rule out the possibility of IUD migration. For patients with IUD combined with lower urinary tract symptoms, it is necessary to be aware of whether IUD perforation affects the bladder.