We describe 3 ovarian and 5 renal anastomosing hemangiomas. One manifested with polycythemia, others were incidental; none recurred. The mean patient age was 58 years. Three hemangiomas developed in end-stage renal disease. Tumors were well-demarcated, mahogany brown, spongy lesions measuring 0.1 to 5 cm. Tortuous large vessels fed and drained tightly packed anastomosing sinusoidal capillary channels. Four hemangiomas exhibited lobular architecture, central edema/hyalinization, and intravascular growth. Five cases had thrombosis, hemorrhage, and hemosiderin. One ovarian tumor induced stromal luteinization. Three tumors had foci of extramedullary hematopoiesis (one associated with polycythemia). Six cases demonstrated eosinophilic intracytoplasmic globules. Three cases included hobnail endothelial cells. Atypia was minimal and mitoses were absent in all cases. We find this vascular neoplasm unique for the genitourinary system. Despite selected features mimicking angiosarcoma, our data support its benign nature. The current study expands the gross and radiographic appearance, clinical aspects, and ultrastructure, with the first report of the lesion occurring in the ovary.