Fifteen patients with isolated old rupture of the anterior cruciate ligament (ACL) were examined to judge their functional disability. The following basic factors were used for evaluation: thigh muscle strength testing, stabilometry in a one-leg stance with straight and flexed knee, gait analysis, performance tests, knee function score, activity grading scale, and clinical joint laxity tests. We found that these rehabilitated patients mainly had impaired performance in those tests which greatly stressed the knee joint's sagittal stability. One-leg hop length was impaired for the injured limb. This group of patients had bilateral impairment of postural control compared with a reference group. This dysfunction was not revealed when comparing limbs. A derotation brace (ECKO) had neither a positive nor a negative effect in the tests. Different aspects of knee function evaluation are emphasized. Some of the altered functions are suggested to be due to central adjustments of motor control.