Bacterial meningitis in adults is a severe disease, with high fatality and morbidity rates. Experimental studies showed that the inflammatory response in the subarachnoid space is associated with unfavorable outcome. In these experiments, corticosteroids, and in particular dexamethasone, were able to reduce the inflammatory cascades in the subarachnoid space. The use of corticosteroids as adjunctive therapy in adults with bacterial meningitis was evaluated in eight studies, performed over 45 years. Most studies on adjunctive dexamethasone therapy in adults with bacterial meningitis suffered from methodological flaws. In 2002, a trial with sufficient study-power to show significant differences was published. This study showed that adjunctive dexamethasone therapy reduced the rate of unfavorable outcomes from 25 to 15% in adults with bacterial meningitis. In this study, adjunctive treatment with dexamethasone was given before or with the first dose of antibiotics, without serious adverse effects. A quantitative review showed a consistent beneficial effect of dexamethasone on mortality and a borderline statistical beneficial effect on neurologic sequels. On the basis of available evidence, adjunctive dexamethasone therapy should be initiated before or with the first dose of antibiotics and continued for four days in all adults with suspected or proven community bacterial meningitis in high-income countries, regardless of bacterial etiology. Since prompt use of dexamethasone and appropriate antibiotics improves the prognosis of adults with bacterial meningitis, hospitals will need protocols to include dexamethasone with the initial antibiotic therapy.