Bartonella (formerly Rochalimaea) quintana is the etiological agent of trench fever, a disease extensively reported during the World Wars. Recent molecular biology approaches have allowed dramatic extension of the spectrum of Bartonella infections. B. quintana is now also recognized as an etiological agent of fever and bacteremia, endocarditis, bacillary angiomatosis, and chronic lymphadenopathy. Human immunodeficiency virus-infected patients and/or homeless people are the most vulnerable to infection. Poverty and louse infestation were the main epidemiological factors associated with B. quintana infections during wartime. Although poverty and chronic alcoholism have been associated with modern cases of trench fever and bacteremia due to B. quintana in Europe and the United States, vectors for B. quintana have not been clearly identified and B. quintana has not been isolated from modern-day lice. Microscopic bacillary angiomatosis lesions are characterized by tumor-like capillary lobules, with proliferating endothelial cells. In vitro experiments have shown that B. quintana survives within endothelial cells and stimulates cell proliferation. These observations, together with the finding that lesions may regress when antibiotic therapy is administered, strongly suggest that B. quintana itself stimulates angiogenesis. Bartonella infections are characterized by a high frequency of relapses after brief courses of antibiotic therapy. It is to be noted that in vitro, although Bartonella species are highly susceptible to antibiotics, only the aminoglycosides have proved to be bactericidal. However, the most effective antibiotic regimen for Bartonella infections remains to be established.