Case summary/ A 7-year-old male castrated domestic shorthair cat presented with a 5-day history of inappetence. A mid-abdominal mass was palpated and, on exploratory laparotomy, a cystic mass arising from the root of the mesentery was observed. The mass was drained, debulked and omentalized. Histopathologic examination and immunohistochemistry supported a diagnosis of hemangiosarcoma. Adjuvant doxorubicin was started and, prior to the third of five doses of doxorubicin, repeat abdominal ultrasound showed complete response of the primary tumor. Continued monitoring 240 days following histopathologic diagnosis revealed suspected metastasis to local lymph nodes, though the primary tumor remained absent on abdominal ultrasound. A second course of five doses of doxorubicin chemotherapy was completed. Serial abdominal ultrasounds demonstrated stable disease in the locoregional lymph nodes with no visible recurrence of the primary tumor. The cat presented 430 days following diagnosis with lethargy and inappetence. Abdominal ultrasound revealed suspected metastatic mesenteric and ileocolic lymphadenopathy, hepatic metastasis and peritoneal effusion, and the owner elected for humane euthanasia. Necropsy findings and negative immunohistochemical staining for lymphatic vessel endothelial receptor-1 were consistent with a metastatic mesenteric hemangiosarcoma. Relevance and novel information Hemangiosarcoma is an uncommon malignancy in cats, and few cases describing treatment have been reported. To our knowledge, this is the first report to describe the use of debulking surgery and adjuvant doxorubicin chemotherapy in the treatment of mesenteric hemangiosarcoma resulting in extended survival in a cat. Multimodal therapy can be considered for the management of cats with mesenteric hemangiosarcoma.