Angiosarcoma most frequently occurs in the skin of the head and neck region of elderly persons, lymphedematous limbs, or in deep soft tissue but only rarely has been described to occur in the female genital tract. Four cases of angiosarcoma of the ovary are described herein. They occurred in patients 25 to 42 years old (median, 31 years). The most common clinical presentation was abdominal pain. All of the tumors were unilateral, hemorrhagic, and ranged from 3.5 cm to 14 cm (median, 13 cm). The histologic appearance of the tumors was varied, and often the vascular nature of the tumor was not apparent immediately. Some of the tumors had a fascicular growth pattern composed of spindle-shaped cells with ovoid nuclei and ample eosinophilic cytoplasm closely mimicking leiomyosarcoma. Other tumors resembled ovarian yolk sac tumor with a reticular growth pattern, whereas, in other areas, cystic structures lined by hobnailed hyperchromatic enlarged nuclei simulated clear cell carcinoma of the ovary. Despite these misleading morphologic findings, all cases were characterized, at least focally, by vasoformative channels or discrete cytoplasmic vacuoles, and all were immunoreactive for vascular markers. Two patients with spread of tumor outside of the ovary died 1 month and 2 years after initial diagnosis, respectively. Two patients with tumor confined to the ovary are alive without evidence of disease 3 and 14 months after diagnosis, respectively. The differential diagnosis of this unusual neoplasm is discussed, and the literature is reviewed.