BACKGROUND:Although intrauterine device (IUD) usage has not been linked to uterine cancer and has even been considered protective against neoplasia, sporadic cases of IUD-associated uterine malignancies have been reported. CASES:One cystic low grade stromal sarcoma of the uterus occurred in a 7-year IUD user, and 1 invasive endometrial squamous cell carcinoma following 25 years of IUD retention occurred in another. The latter case was notable for extensive in situ squamous cell carcinoma involving the entire uterine cavity and extending to the ectocervix and into both fallopian tubes. In situ hybridization for high-risk HPV DNA was negative. These findings raise the possibility of a non-HPV-related pathway for the squamous cell carcinoma case due possibly to prolonged chronic irritation and pyometra. CONCLUSION:The association of low grade stromal sarcoma with the IUD in the first case is extremely rare and most likely coincidental. The squamous carcinoma case, however, may have arisen via a non-HPV-related pathway, possibly related to IUD-induced chronic irritation and pyometra.