Uterine artery embolization (UAE) as an alternative to surgery for the treatment of uterine fibroids and adenomyosis uteri became increasingly popular. While the clinical success of this new treatment strategy is without doubt, there is still considerable uncertainty with respect to the morphologic changes induced by UAE. In this study, a total of 173 women were treated with UAE using tris-acryl gelatin microspheres (TGMS), a new particulate spherical embolic agent, for either symptomatic adenomyosis or leiomyoma. Surgical specimens of 8 women who underwent subsequent myomectomy or hysterectomy were evaluated by conventional histology and immunohistochemistry. TGMS were readily apparent in both macroscopy and routine histology. In patients with fibroids, TGMS accumulated in medium-sized vessels in the direct tumor vicinity, a minor fraction of particles was detected in the outer half of the myometrium and within leiomyomata. In patients with adenomyosis, a random distribution of TGMS was noted throughout the outer half of the myometrium. Freshly infused particles occluded the respective arteries without a significant tissue reaction. In the course of time, a granulomatous foreign body reaction in the vicinity of particles occurred, eventually followed by complete vessel destruction. Leiomyoma treated with UAE showed either hyaline necrosis, coagulative necrosis, or no change at all. Foci of adenomyosis remained unaltered. In conclusion, after UAE with TGMS, particles were identified predominately but not exclusively at the periphery of fibroids. Pathologists must be aware of the morphologic changes induced by UAE in leiomyoma to avoid misinterpretation of induced tissue alterations as signs of malignant tumor growth.