Although postoperative septic arthritis is rare after ACL reconstruction, it carries a high morbidity that results in poor clinical outcome. Despite low incidence, it is important to recognize that infection and treat it without delay because of devastating consequences, such as loss of hyaline cartilage and arthrofibrosis, in order to avoid osteoarthritis development and near full range of motion achieved. Herein we discuss the pathogenesis, risk factors, clinical presentation, diagnostic evaluation, treatment protocols and complications of septic knee arthritis after ACL reconstruction.