Overall mortality for 142 patients with Bacteroides bacteremia encountered in the four hospitals of one metropolitan area between 1977 and 1982 was 41%. Only 43% of deaths of these patients, however, were attributed directly to Bacteroides infection according to the criteria used in this study. Deaths of patients with Bacteroides bacteremia, compared with deaths of patients with bacteremia due to aerobic gram-negative rods, were less likely to occur early after onset of bacteremia. Choice of antimicrobial therapy had no obvious relationship to eventual outcome. Nonobstetrical Bacteroides bacteremia identifies a group of patients at high risk of death during hospitalization. The diversity of both clinical and microbiologic features of these infections, however, makes specific recommendations regarding optimum therapy difficult to formulate.