Lactobacillus species are ubiquitous inhabitants of the human gastrointestinal and genitourinary tracts and rarely cause infections. Pneumonia caused by Lactobacillus has been reported only in immunocompromised patients and in one patient with structural lung disease. A 39-year-old, immunocompetent, critically ill woman developed ventilator-associated pneumonia, which was found to be caused by Lactobacillus. To our knowledge, this is the first such report. The infection was treated successfully with 14 days of intravenous vancomycin. Based on this case, Lactobacillus should be considered a possible cause of ventilator-associated pneumonia in immunocompetent, critically ill patients.