Hemangiosarcoma is an uncommon neoplasm in horses that often presents with non-specific signs and is rarely diagnosed antemortem.1 This paper summarizes the case of a horse with disseminated hemangiosarcoma for which a presumptive antemortem diagnosis was made less than 24 hours after admission to Cornell University’s Equine and Farm Animal Hospital based on cytology. The characteristic clinical presentation, most common diagnostic findings, and outcomes of surgical treatment of horses with hemangiosarcoma are reviewed.