Septic arthritis of the knee is a potentially life-threatening condition and can be associated with many late complications. The key of success of management of septic arthritis of the knee joint is early aggressive treatment of surgical debridement and decompression and antibiotic therapy. In adults, arthroscopic drainage with synovectomy is the treatment of choice in septic arthritis of the knee, with lower rates of infectious recurrence than needle aspiration and better functional results than open surgery. Repeated arthroscopic debridement and drainage is needed in case of delayed treatment with an advanced arthroscopic stage of the infection, early unfavorable course, or multiresistant germ. In these situations, synovectomy should be as complete as possible to maximize the reduction of the bacterial burden and avoid the need of further debridement. The purpose of this Technical Note is to describe the details of complete arthroscopic synovectomy of the knee joint. This includes 2 circles of circumferential synovectomy. One circle is in the axial plane and includes the intercondylar notch, anterior, posterior, medial, and lateral compartments. The other circle is in the coronal plane and includes the supra-patellar pouch, medial and lateral recesses, and the anterior compartment.