['Optimal antibiotic treatment strategies of Haemophilus infections are still needed. Therefore, 30-day case fatality rate (CFR) of Haemophilus bacteremia and efficacy of various antibiotic treatment regimes were studied.', 'All episodes of Haemophilus bacteremia in the former Copenhagen County during the period 2000-9 were included in the study. Clinical and biochemical findings and outcome were collected retrospectively from medical records.', '105 consecutive episodes were identified (median age: 69\u2009years, with only 4 children <16\u2009years), 72% were due to non-typeable -, 16% to typeable H. influenzae, and 11% to other Haemophilus species. Pneumonia was the most common primary focus (in 48%), and 58% of the patients had Charlson comorbidity index\u2009>\u20091. Definitive antibiotic therapy was in 26 cases benzylpenicillin, in 12 cases aminopenicillins, in 50 cases cefuroxime and in 16 cases broadspectrum antibiotics, whereas 1 palliative case died without start of therapy. Whereas the use of broadspectrum antibiotics was related to the severity of the disease (admittance to ICU, need for assisted ventilation or hemodialysis, septic shock), no significant difference in clinical features was demonstrated for therapy with benzylpenicillin, aminopenicillin or cefuroxime, except benzylpenicillin was rarely administered to immunosuppressed patients. The CFR was 22% (23/105). The choice of empiric antibiotic therapy was not significantly associated with mortality (adequate vs. inadequate treatment: 23% (21/93) vs. 17% (2/12), respectively, P\u2009>\u20090.05). In contrast, definite antibiotic therapy with cefuroxime or aminopenicillins resulted in a significantly lower CFR than treatment with benzylpenicillin (12% (6/50) or 0% (0/12) vs. 39% (10/26), respectively, Log rank test P\u2009<\u20090.02). When adjustments were made for other identified risk factors in bivariate logistic regression analysis, treatment with cefuroxime was still were found to be associated with a significantly lower CFR than for benzylpenicillin: OR: 0.21 (0.06-0.69), P\u2009=\u20090.01 (hospital-acquired bacteremia), OR: 0.27 (0.08-0.91), P\u2009=\u20090.04 (polymicrobial episodes), OR: 0.16 (0.04-0.59), P\u2009=\u20090.006 (admittance at intensive care unit), OR: 0.22 (0.06-0.82), P\u2009=\u20090.02 (alcohol abuse), OR: 0.15 (0.04-0.60), P\u2009=\u20090.008 (altered mental state), OR: 0.22 (0.07-0.71), P\u2009=\u20090.01 (temperature\u2009<\u200938\u2009°C), OR: 0.23 (0.07-0.79), P\u2009=\u20090.02 (septic shock), OR: 0.21 (0.06-0.69), P\u2009=\u20090.01 (mechanical ventilation).'] Is treatment of Haemophilus bacteremia with benzylpenicillin associated with increased ( 30-day ) mortality?