The treatment of infections caused by Acinetobacter baumannii has become increasingly complicated due to the emergence of highly resistant strains. In the present study we demonstrate that immunization with an inactivated whole cell vaccine elicits a robust antibody response that provides protection against challenge with multiple A. baumannii strains in a murine model of disseminated sepsis. In addition, we show that passive immunization with serum raised against inactivated cells protects mice from subsequent infection. These results demonstrate that active and passive immunization using an inactivated whole cell vaccine may be an effective approach for preventing infection by A. baumannii.