Polymicrobial bacteraemia involving Streptococcus pneumoniae and other bacteria (e.g. Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Haemophilus influenza, viridans streptococci, Salmonella spp.) occurred in 3.4% of our pneumococcal bacteraemia cases. Compared with 308 controls (monomicrobial bacteraemia), the 77 polymicrobial cases included more males (83 vs 62%, p = 0.001), had serious underlying diseases (100 vs 80%, p < 0.001), abdominal infection (18 vs 5%, p < 0.001), nosocomial infection (33 vs 8%, p < 0.001), shock (40 vs 13%, p < 0.001), and higher mortality (52 vs 18%, p < 0.001). Clinicians must be aware that some patients with pneumococcal bacteraemia may have other bacteria in their blood, which would confer higher mortality and may lead to inappropriate or incomplete antibiotic therapy.