Three cases of angiosarcoma in the stomach, small bowel, and colon, respectively, are reported. The gastric lesion occurred many years after historic evidence of cutaneous Kaposi's sarcoma. Two of the three lesions exhibited multifocality, and all demonstrated aggressive biologic courses. The varied histologic features of angiosarcoma make this diagnosis difficult to establish in an unusual location such as the gastrointestinal tract. The use of immunohistochemistry for a panel of antibodies, particularly the successful reaction with Factor VIII-related antigen, is important in evaluating light microscopically unusual tumors. A delicate framework of collagen type IV was elicited in each case, but ultrastructurally correlated with short segments of basal lamina in one case. This suggests that the absence of the traditional morphologic expression of basal lamina does not preclude its presence and emphasizes the sensitivity of immunohistochemistry. The lack of previously reported cases of gastrointestinal angiosarcoma may be because the tumor is underrecognized or because it is truly a rare occurrence.