The acquired immunodeficiency syndrome and other causes of immunosuppression have ushered in a variety of opportunistic infections. One of these is bacillary angiomatosis, a vasoproliferative lesion whose principal causative agent is Rochalimaea henselae. Bacillary angiomatosis, while preponderantly a cutaneous affliction, can be systemic, including involvement of the head and neck mucous membranes. Molecular technology and epidemiologic studies used to identify the bacterial agent of bacillary angiomatosis have also uncovered R henselae as the organism responsible for most cases of cat-scratch disease. Why the same organism promotes two different histopathologic lesions, as seen in bacillary angiomatosis and cat-scratch disease, is unknown.