In spite of considerable success in the development of drugs and vaccines, the problem of disease due to Neisseria meningitidis is far from solved. As late as the 1970s, epidemics of meningococcal disease occurred in at least 30 countries in all parts of the world. Most of the epidemics were caused by group A organisms, but epidemics due to groups Band C also took place occasionally. The case/fatality rate was usually <10070 among patients with true meningitis; among those with “pure” septicemia, it was as high as 70%. Children less than five years old are most prone to meningococcal disease, but mortality is often highest among young adults. Because close contacts of the index case are at considerable risk - at least several hundred times higher than in the rest of the population - they should be protected immediately with an appropriate antibiotic and, if possible, with a vaccine as well. At the present time, however, no vaccine is available for use against group B organisms, which in nonepidemic conditions are the most prevalent of all meningococci.