External adenomyosis refers to deep infiltrative endometriosis (DIE) arising within the outer myometrium/uterine serosa with a variable depth of the invasion of the myometrium but with an intact junctional zone. It has been recently introduced into the literature as a separate entity to describe in MRI. Even if the spelling contains the term adenomyosis, external and internal adenomyosis are different conditions. External adenomyosis is highly associated with DIE or with endometriomas. The by far more common posterior type of external adenomyosis is almost always found in association with extensive DIE of the posterior compartment. Anterior external adenomyosis is typically found with or without continuity to DIE of the bladder, the uterovesical fold, or the round ligaments. Having exact information on the location, extent, and severity is an important criterion for treatment decisions.