Posterolateral rotatory instability of the knee, usually accompanied by other instabilities, is easily missed, misdiagnosed, and mistreated. The correct diagnosis requires a complete examination of the knee, including both the external rotation-recurvatum and posterolateral drawer tests. The most effective operative approach when the lesion is interstitial or at the site of the femoral attachment consists of advancing the arcuate ligament complex and its osseous attachment anteriorly and distally on the femur to support the arcuate ligament repair. When the lesion is distal and the arcuate ligament attachment to the tibia and fibula is loose, this area must be stabilized. In a consecutive series of 140 patients, 141 knees were reconstructed with this procedure. Ninety-five patients (ninety-six knees), with a follow-up of two to thirteen years, form the basis for this report. Seventy-one of the patients had undergone a combined total of 112 prior operations on the knee without functional recovery. After surgery directed at the arcuate ligament complex, eighty-two knees (85 per cent) were objectively rated as good; thirteen (14 per cent), as fair; and one, as poor. Subjectively, seventy-five (78 per cent) of the patients considered the result to be good; twenty-one (22 per cent), fair; and none, poor. Functionally, seventy-seven (80 per cent) of the knees were rated by the patient as good; sixteen (16 per cent), as fair; and three (4 per cent), as poor. This is the first report on the long-term results of reconstruction of the arcuate ligament complex for the correction of chronic posterolateral rotatory instability. The results demonstrate the effectiveness of the procedure.