Although the trend in management of tibial plateau fractures has been toward early motion, the period of immobilization that can be tolerated safely is open to question. In the present study, 160 acute tibial plateau fractures were reviewed in an effort to answer this question. The 112 fractures that were suitable for analysis were divided into undisplaced fractures, displaced fractures treated nonoperatively, and displaced fractures treated operatively. Among these groups, results were compared based on the period after injury that the knee was immobilized. Undisplaced fractures and displaced fractures that were treated nonoperatively regained full knee motion when immobilized up to six weeks. Fractures treated operatively tended to develop knee stiffness with only two weeks of immobilization. Loss of fracture reduction tended to occur in patients who were immobilized for relatively short periods. Immediate knee motion was correlated with prolonged hospitalization. Based on these results, knee mobilization following tibial plateau fractures is determined by the degree of fracture displacement, method of treatment, and quality of aftercare.