We performed a retrospective study of knee joint infections after arthroscopic anterior cruciate ligament reconstruction at our institution. Two thousand five hundred anterior cruciate ligament reconstructions were performed between 1988 and 1993. Seven (0.3%) patients experienced postoperative deep infections of the knee. All anterior cruciate ligament reconstructions were performed using arthroscopically assisted techniques. Six (86%) of these patients had concomitant open procedures performed, including meniscal repair, posterolateral corner reconstruction, and medial collateral ligament reconstruction. Four patients had acute (< 2 weeks), two patients had subacute (2 weeks to 2 months), and one patient had late (> 2 months) infections. All patients had positive cultures from knee joint aspirates with the organisms Staphylococcus aureus, Staphylococcus epidermidis, Peptostreptococcus, or a combination thereof. All patients underwent immediate arthroscopic irrigation and debridement. All infections were intraarticular; six patients also had extraarticular sites of infection. Four patients underwent repeat irrigation and debridement at approximately 1 week. The anterior cruciate ligament graft was removed from four patients. All patients were treated with intravenous antibiotics for 4 to 6 weeks, protected weightbearing, and physical therapy. At a mean followup of 29 months, mean knee extension was 0 degree, and mean knee flexion was 122 degrees (range, 70 degrees to 135 degrees). Six (86%) patients had minimal to no pain in their operative knee, and they were satisfied with their functional results.