A 39-year-old woman undergoing immunosuppressive therapy following kidney transplantation for systemic lupus erythematosus presented with a uterine adenomatoid tumor that diffusely infiltrated the entire myometrium and contained a serosal papillary cystic component that resembled a cystic mesothelioma. This is the first reported case of an adenomatoid tumor showing both of these features. Although adenomatoid tumors are considered benign, the patient may be at risk for recurrence of the papillary cystic component (which is known to recur in 50% of cases) if this tumor reflects an inability to limit neoplastic processes.