We evaluated the ability of three functional knee braces, (CTI, OTI, and TS7) to control anterolateral rotary instability of the knee. Fourteen subjects, none of elite athletic status, with arthroscopically proven anterior cruciate deficient knees were selected. The subjects evaluated each brace after one-month periods, and then underwent testing with physical examinations, KT-1000 arthrometry, and timed running events. All braces reduced subjective symptoms of knee instability. Different subjects preferred different braces. KT-1000 testing showed a reduction in anterior tibial displacement for all braces; however, this reduction did not increase as forces increased. A timed figure-of-eight running event did not show any functional advantage of bracing. Five subluxation events occurred in four subjects while braced. Functional braces appear to have a role in the anterior cruciate deficient knee, but only in conjunction with activity modification.