Hemangiosarcoma was diagnosed in 31 cats. Diagnosis was confirmed by surgical biopsy. Locations of the primary tumors were the abdominal cavity (15 cats), sc tissue (13 cats), thoracic cavity (2 cats), and nasal cavity (1 cat). Nine (60%) of the 15 cats with abdominal hemangiosarcoma had extrathoracic evidence of metastasis: this was not found in the other cats. Of the cats with tumors located in the sc tissue, 6 of 10 (60%) evaluated on a long-term basis had local recurrence of the tumor. Eleven cats were not available for follow-up evaluation, 3 cats were euthanatized at the time of surgery, and 2 others were euthanatized within the first postoperative week subsequent to histologic diagnosis of hemangiosarcoma. Of the remaining 15 cats, 4 with abdominal hemangiosarcoma and 5 with hemangiosarcoma of the sc tissue died at means of 22 and 44 weeks, respectively.