A 32-year-old, pluriparous, oriental horse breed mare was presented to the Veterinary Teaching Hospital of the Veterinary Medical School of Messina, with clinical symptoms characterized by vulvar blood drainage for suspicious abortion. Ultrasonographic examination showed the presence of blood in uterine body and a complex-mass structure, echo dense with cystic areas with anechoic content at the basis of the right horn. Uterine leiomyoma was suspected, a partial ovary hysterectomy was proposed to the owner; despite this, the owner refused to submit the mare to surgery. The mare spontaneously died after 18 months, and necropsy was performed. At macroscopic postmortem examination, the right uterine horn showed a well-demarcated pedunculated nodular bulge, variegated in color with large hemorrhages (22 × 18 × 15 cm), and a capsulated sessile nodule (7 × 4 × 3 cm) involving the smooth uterine musculature. Histologic analysis suggested a diagnosis of subserosal leiomyoma (large mass) and submucosal intramural leiomyoma (small nodule).