Lactobacillus is a Gram positive bacteria found in the mouth, gastrointestinal and female genital tract. Serious infections due to Lactobacillus are becoming increasingly common. We present a 49-year-old diabetic patient with Lactobacillus septic arthritis. To our knowledge, this is the first reported case. Usually, Lactobacillus is implicated with bacteremia, endocarditis and more rarely pneumonia, meningitis and endovascular infection, and half of the cases are reported in immunocompromised patients. As in our patient, diabetes mellitus is a comorbid condition which has been clearly noted. Our finding suggests that further studies are necessary to establish the significance of Lactobacillus as an etiologic agent of septic arthritis.