OBJECTIVE:To study the effects of an increase in task complexity on brake response time (BRT) in patients undergoing total knee arthroplasty (TKA). DESIGN:A prospective repeated-measures design was used. The measurements took place 1 day before and 10 and 30 days after surgery. SETTING:Clinic. PARTICIPANTS:The data of patients (N=21) who were admitted for primary total arthroplasty of the right knee were pooled for analysis. INTERVENTIONS:On each measurement day patients performed 5 practice and 10 test trials for 2 tasks (1 simple, 1 complex) in a car simulator. Task complexity was increased by adding a second movement to the first task performed. MAIN OUTCOME MEASURES:BRT, reaction time (RT), and movement time were assessed. RESULTS:An increase in task complexity increased BRT, RT, and movement time at all measurement times. Right TKA increased BRT by increasing movement time. Thirty days after surgery BRT was no longer increased compared with preoperative values in both tasks. CONCLUSIONS:Task complexity consistently increased BRT and its components. The effects of task complexity remained constant throughout the 3 measurements. After right TKA, we suggest patients should be advised to wait 30 days after surgery before resuming driving.