The diagnosis of bacterial meningitis may be established through positive blood cultures in cases with negative culture of cerebrospinal fluid (CSF). However, information is sparse regarding how often the aetiological diagnosis is determined by blood culture alone. Therefore, we undertook a retrospective study of patients with meningitis and a blood culture-based bacterial diagnosis in North Jutland County, Denmark in 1997-2005. Patients were included if they had 1) a microscopy- and culture-negative CSF specimen with a leukocyte count > or =100x10(6)/l and an erythrocyte count < or =10,000x10(6)/l and 2) a positive blood culture within an interval of 3 d. A total of 20 patients fulfilled these criteria: 7 with Streptococcus pneumoniae, 4 with Neisseria meningitidis, 4 with Staphylococcus aureus, and 5 with miscellaneous bacteria. Suitable antibiotic therapy was delayed up to 48 h after lumbar puncture, and in-hospital mortality was 25%. A discharge diagnosis of bacterial meningitis was missing in 6/20 cases, and 12/20 cases had not been reported to Danish health authorities. Thus, patients with CSF-culture negative bacterial meningitis are at risk of delayed therapy, a poor outcome, and incomplete notification to health authorities.