Background: A population-based nested case-control study was conducted in order to characterize patient factors and microbial species associated with recurrent bacteraemia. Methods: All patients with bacteraemia in a Danish region during 1996-2006 were investigated. Recurrence was defined based on pathogen identity, site of infection and time frame, and not restricted to homologous pathogens. Results: We identified 8672 patients with first-time bacteraemia, of whom 1003 (12%) had a recurrence within 1 year. The proportion of mono-microbial bacteraemia was similar for first (86%) and recurrent episodes (84%). An unknown focus was common in both episodes (22.7 and 29.1%, respectively). Independent predictors of a recurrence (incidence rate ratio, 95% confidence interval) included health care-associated (2.4; 1.9-3.0) and nosocomial bacteraemia (2.1; 1.8-2.6), poly-microbial Gram-positive bacteraemia (2.7; 1.6-4.6), and fungaemia (2.2; 1.4-3.5), a Charlson co-morbidity index score of 1-2 (1.7; 1.4-2.1), inappropriate empirical antimicrobial chemotherapy (1.3; 1.1-1.5), a gastro-intestinal tract focus (2.3; 1.7-3.0), a liver/biliary tract focus (2.7; 2.0-3.6), an iv-catheter focus (2.0; 1.4-2.8), endocarditis ( 2.7; 1.6-4.3), and an unknown focus (1.9; 1.5-2.3). Conclusions: This study showed recurrent bacteraemia to be common and the following risk factors were identified: a health care-associated or nosocomial origin, poly-microbial or fungal aetiology, a focus within the abdomen, endocardium, iv-catheter-related or unknown, a Charlson co-morbidity index score of >1 and inappropriate empirical antimicrobial chemotherapy. (C) 2010 The British Infection Society. Published by Elsevier Ltd. All rights reserved