Osteoarthritis (OA) is the most common indication for total knee arthroplasty (TKA), but the rate of contralateral disease progression after unilateral TKA as well as risk factors that may predict progression have not been determined. We assessed the overall rate of contralateral knee replacement after initial TKA for OA as a marker of progression to advanced symptomatic OA.A total of 117 consecutive patients undergoing unilateral TKA for OA between 1983 and 1988 were evaluated and followed longitudinally for up to 14 years. Evaluation of potential risk factors for progression to contralateral TKA included age, sex, side of surgery, body mass index (BMI), and Kellgren-Lawrence (K-L) grade.The contralateral knee progressed to TKA in 31 patients, yielding an overall 10-year risk of contralateral TKA of 37.2%. The baseline K-L grade of the contralateral knee was strongly correlated with future risk of TKA (p < 0.001). Mean survival times were similar for those with grade II (131.7 mo) and grade III (127.6 mo); patients with grade IV, however, had a mean survival of 80.5 months, with an overall 10-year risk of TKA of 62.7%. Age, sex, side of initial TKA, and BMI were not risk factors for progression to contralateral TKA.In this cohort, the K-L grading scale was a highly significant predictor for progression of contralateral OA to TKA. These data may provide important information to patients undergoing TKA, and shed light on the natural history of contralateral OA after TKA.