Interleukin (IL)-17A affects the immune system of the lung. Legionella infection can potentially lead to severe pneumonia. The present study aimed to evaluate the role of IL-17A in Legionella pneumonia. Serum IL-17A levels were quantified in both patients with Legionella pneumonia and control subjects; IL-17 was detected in sera from 4 out of 31 patients with Legionella pneumonia but in any controls. There were no differences in peripheral white blood cell counts or other serum biomarkers (C-reactive protein, and lactate dehydrogenase) between IL-17A-positive and IL-17A-negative patients. All IL-17A-positive patients in this cohort survived, where 8 of 27 IL-17A-negative patients did not. IL-17A was detected in available bronchoalveolar (BA) fluid samples from 7 patients with Legionella pneumonia within our cohort. However, the IL-17A and IFN-γ concentrations in BA fluids did not correlate with each other. IL-17A might play a significant role in some cases of Legionella pneumonia.