Now that invasive disease caused by Haemophilus influenzae type b has been largely controlled in the developed world, the principal bacterial pathogen causing meningitis in most countries is the meningococcus. Serogroup B and C strains predominate in most industrialised countries in contrast to the situation in sub-Saharan Africa, where serogroup A meningococcal disease is periodically a problem of massive epidemic proportions. This review focuses on developments in our understanding of the diagnosis and treatment of meningococcal disease, of host factors important in susceptibility to, and severity of, this infection, and on advances which may eventually lead to its prevention.