Angiogenesis is required for tumor growth, and the degree of new vessel formation correlates with adverse prognosis in many types of malignancies. It has now been appreciated that tumor-associated vasculature is heterogenous and sometimes includes a complex vasoformative process that has been termed florid vascular proliferation or glomeruloid microvascular proliferation. These vascular lesions are most characteristic of high-grade gliomas and neuroendocrine tumors but are being increasingly recognized in other types of neoplasias as well. Herein we report a case of carcinosarcoma arising within the cecal wall of a 62-yr-old patient that exhibited florid vascular proliferation, particularly at the time of peritoneal recurrence. Recognition of these tumor-associated vasoformative lesions may be important in view of their adverse prognostic association and may become therapeutically relevant considering the current developments in angiogenesis inhibitors.