We assessed the frequency and clinical significance of polymicrobial infections in 31 patients with sporadic community-acquired Legionella pneumonia. Twenty-six patients were men, 5 were women and mean age was 61 years. Eighteen patients were smokers, 6 patients were chronic alcoholics and 23 had underlying diseases. Regarding severity, the illnesses were mild (two patients), moderate (seven patients) and severe (twenty-two patients). In 9 (29%) of the patients, one other etiologic agent for community-acquired pneumonia was identified in addition to the Legionella species. The distribution of one other causal agent was as follows: Mycoplasma pneumoniae, 2 patients; Chlamydia pneumoniae, 2; Chlamydia psittaci, 1; Influenza virus, 1; Streptococcus pneumoniae, 1; Klebsiella pneumoniae, 1; Pseudomonas aeruginosa, 1 patient. Because an antimicrobial agent with activity against Legionella species can also provide coverage for Mycoplasma pneumoniae. Chlamydia pneumoniae, and Chlamydia psittaci, the patients with these coinfections improved without any complications. The patient with influenzavirus coinfection became seriously ill, and the condition was complicated by disseminated intravascular coagulation, renal failure and aspergillus bronchitis. The case of Pseudomonas aeruginosa coinfection was accompanied with a lung abscess and empyema. Our experience illustrates the importance of considering polymicrobial infections in patients with sporadic community-acquired Legionella pneumonia.