Survival analysis studies of 40 patients treated with high tibial osteotomy for arthritis with angular deformity were performed to determine the dominant factors that adversely affected long-term knee function. Obesity, advanced age, and postoperative overcorrection or undercorrection resulted in short durations of successful function. On the average, the probabilities for continued useful function of the knee at tested intervals were: one year, 86%; three years, 64%; five years, 50%; and nine years, 28%.