This report presents a case of intravascular lymphomatosis identified within an angiolipoma. The patient was a 73-year-old woman with a history of lobular carcinoma of the breast who presented with a chest wall nodule near the site of prior mastectomy. Microscopically, the nodule was composed of encapsulated adipose tissue with an associated vascular proliferation. Many of the vascular lumina were expanded by collections of large pleomorphic cells with vesicular nuclei and prominent nucleoli. These atypical cells displayed immunoreactivity for CD45RB (leukocyte common antigen) and the pan-B cell marker CD20 (L26). The patient subsequently developed multiple lesions of the extremities and died soon after developing symptoms referable to the central nervous system. Intravascular lymphomatosis most commonly presents with central nervous system and dermatologic involvement although any organ system may be affected. Intravascular lymphomatosis is an aggressive neoplasm that is generally diagnosed at postmortem examination. This case shows the protean manifestations of intravascular lymphomatosis and highlights the necessity of considering this malignancy in the differential diagnosis when entertaining the diagnosis of vascular invasion by carcinoma. Ann Diagn pathol 5:103-106, 2001. This is a US government work. There are no restrictions on its use.