Posteromedial subluxation has been reported as a mode of failure with flat-on-flat articular geometry. Medical records were reviewed to find patients who developed progressive subluxation of the femur. From a consecutive series of 2,773 primary anatomically graduated components (AGC) knees, 6 patients developed progressive posterior subluxation of the femur. The mean interval between the index total knee arthroplasty (TKA) and the diagnosis of subluxation was 4.8 years. Five cases were revised at an average of 6.2 years after index TKA. Tightness of the posterior cruciate ligament (PCL) was observed in all revised cases. Progressive posterior subluxation is a rare complication after AGC knees. It is believed that the primary factor causing progressive subluxation is tightness of the PCL. The PCL should be recessed if PCL tightness is seen at surgery.