Chronic and recurrent bone infections occur frequently but have not been explained.Staphylococcus aureus(S. aureus) is often found among chronic and recurrent infections and may be responsible for such infections. One possible reason is thatS. aureuscan internalize and survive within host cells and by doing so,S. aureuscan evade both host defense mechanisms and most conventional antibiotic treatments. In this study, we hypothesized that intra-cellularS. aureuscould induce infectionsin vivo. Osteoblasts were infected withS. aureusand, after eliminating extra-cellularS. aureus, inoculated into an open fracture rat model. Bacterial cultures and radiographic observations at post-operative day 21 confirmed local bone infections in animals inoculated with intra-cellularS. aureuswithin osteoblasts alone. We present directin vivoevidence that intra-cellularS. aureuscould be sufficient to induce bone infection in animals; we found that intra-cellularS. aureusinoculation of as low as 102 colony forming units could induce severe bone infections. Our data may suggest that intra-cellularS. aureuscan “hide” in host cells during symptom-free periods and, under certain conditions, they may escape and lead to infection recurrence. Intra-cellularS. aureustherefore could play an important role in the pathogenesis ofS. aureusinfections, especially those chronic and recurrent infections in which disease episodes may be separated by weeks, months, or even years.