It has been suggested that bacillary (epithelioid) angiomatosis (BEA) is a manifestation of cat scratch disease (CSD). Because of clinical similarity between this condition and the verruga peruana phase of bartonellosis, we sought to further characterize this disease as well as its causative agent and to compare it to bartonellosis. We isolated a small flagellated pleomorphic bacillus from skin lesions of two patients with BEA. Organisms were stained successfully with Warthin-Starry silver stains, but immunohistochemistry failed to demonstrate binding with a polyclonal antibody directed against the cat scratch bacillus. Whole cell fatty-acid gas chromatography performed on both BEA organisms and Bartonella bacilliformis demonstrated marked similarity between the two. Electron microscopy of BEA organisms in tissue and in suspension revealed features characteristic of a gram negative bacillus. Based on these findings, we propose that this unusual rickettsial infectious disease with vascular proliferation may represent an unusual variant of infection with a bartonella-like organism rather than a manifestation of cat scratch disease.