To the Editor: Polymicrobial invasive infections are infrequent, representing <10% of the invasive infections of known etiology (1). They are often correlated with a predisposing factor: immunodeficiency (e.g., diabetes mellitus, malignancies, extremes of age) or use of a central catheter. Escherichia hermanii is an extremely rare etiologic agent for invasive infections; only four cases were published from 1980 to 2002. We report the first case of double invasive infection by E. hermanii and Staphylococcus aureus and emphasize the importance of screening of all the septic foci for demonstrating a polymicrobial invasive infection.