Uterine adenosarcomas are uncommon mixed Müllerian neoplasms, most commonly arising in the uterine corpus. A new Federation of International Gynecologic Organization staging system for these tumors has recently been implemented. This staging system is an improvement on the earlier generic application of the 1988 Federation of International Gynecologic Organization staging system for endometrial cancer to adenosarcoma. Herein, we report 3 uterine adenosarcomas with unusual features. For 2 of these, no specific staging guidelines are provided by either the earlier or, more importantly, the new staging system. The first case is of an adenosarcoma arising in the eutopic endometrium with involvement of underlying adenomyosis without myometrial invasion; the second originated in a mural adenomyoma in the absence of eutopic endometrial involvement; and the third case encompassed synchronous endometrial and extrauterine (peritoneal) neoplasms. Such cases are rare, and there is insufficient evidence to be definitive about staging. Thus, we suggest a descriptive reporting strategy for adenosarcomas with these unusual features. We also propose a reporting nomenclature for such cases to ensure standardization such that they can be adequately recorded in synoptic reporting protocols. This will facilitate reliable data collection such that an evidence-based staging system for these scenarios may be derived.