Objective: To review the evidence for effectiveness of treatment with antibiotics before admission in reducing case fatality from meningococcal disease. Design: Systematic review. Data sources: Cochrane register of trials and systematic reviews, database of abstracts of reviews of effectiveness, health technology assessment, and national research register in England and Wales, Medline, Embase, and CAB Health. Included studies: Studies describing vital outcome of at least 10 cases of meningococcal disease classified by whether or not antibiotics were given before admission to hospital. Results: 14 observational studies met the review criteria. Oral antibiotic treatment given before admission was associated with reduced mortality among cases (combined risk ratio 0.17, 95% confidence interval 0.07 to 0.44). In seven studies in which all included patients were seen in primary care, the association between parenteral antibiotics before admission and outcome was inconsistent (χ2 for heterogeneity 11.02, P = 0.09). After adjustment for the proportion given parenteral antibiotics before admission, there was no residual heterogeneity. A higher proportion of patients given parenteral antibiotics before admission was associated with reduced mortality after such treatment and vice versa (P = 0.04). Conclusion: Confounding by severity is the most likely explanation both for the beneficial effect of oral antibiotics and the harmful effect observed in some studies of parenteral antibiotics. We cannot conclude whether or not antibiotics given before admission have an effect on case fatality. The data are consistent with benefit when a substantial proportion of cases are treated.