Patellofemoral instability following total knee arthroplasty remains one of the major complications requiring operative intervention. In spite of recent advances in technique and instrumentation, the rate of this complication remains disturbingly high. A comprehensive analysis of cause reveals malalignment of any of the components to be potentially responsible, particularly valgus or internal rotation malalignment of either femoral or tibial component, as well as lateral displacement of the patellar component. Underresection of the patella or oversizing the femoral component may also contribute to excessive lateral retinacular tightness. When confronted with patellofemoral instability, the surgeon must first look for and correct the cause. Component malalignment requires component revision. Extensor mechanism imbalance requires either proximal or distal realignment. Lateral release alone invites recurrence of the problem.