Lactobacilli are ubiquitous gram-positive anaerobic rods present in the normal bacterial flora of the mouth, vagina and gastrointestinal tract. Although they are usually non pathogenic, serious infections have occasionally been described in transplant recipients or severely ill patients. Only 4 cases have been reported involving AIDS: one had predisposing conditions other than AIDS, and none of the others had pure growth of lactobacilli. We report a case of community-acquired Lactobacillus casei pneumonia in a CD4 lymphocyte-depleted AIDS patient. Lactobacillus was isolated in pure growth in repeated blood cultures in an outpatient with no preexisting lung diseases and no known risk factors for Lactobacillus infections (dental procedures, complicated deliveries, gastrointestinal diseases, cardiac prosthetic valves) or consumption of unusual dairy products. Although uncommon, lactobacilli are possible pathogens in HIV-infected patients with very low CD4 counts, and their isolation in clinical specimens must not be neglected. Susceptibility tests are essential because of the variable antibiotic-resistance patterns of these bacteria.