Bacterial meningitis is uncommon but causes significant mortality and morbidity, despite optimum antibiotic therapy. A clinical trial in 301 patients showed a beneficial effect of adjunctive steroid treatment in adults with acute community-acquired pneumococcal meningitis, but data on other organisms or adverse events are sparse. This led us to do a quantitative systematic review of adjunctive steroid therapy in adults with acute bacterial meningitis. Five trials involving 623 patients were included (pneumococcal meningitis=234, meningococcal meningitis=232, others=127, unknown=30). Overall, treatment with steroids was associated with a significant reduction in mortality (relative risk 0.6, 95% CI 0.4-0.8, p=0.002) and in neurological sequelae (0.6, 0.4-1, p=0.05), and with a reduction of case-fatality in pneumococcal meningitis of 21% (0.5, 0.3-0.8, p=0.001). In meningococcal meningitis, mortality (0.9, 0.3-2.1) and neurological sequelae (0.5, 0.1-1.7) were both reduced, but not significantly. Adverse events, recorded in 391 cases, were equally divided between the treatment and placebo groups (1, 0.5-2), with gastrointestinal bleeding in 1% of steroid-treated and 4% of other patients. Since treatment with steroids reduces both mortality and neurological sequelae in adults with bacterial meningitis, without detectable adverse effects, routine steroid therapy with the first dose of antibiotics is justified in most adult patients in whom acute community-acquired bacterial meningitis is suspected.