We did a retrospective review and follow-up examination to investigate the incidence, risk factors, and outcome of patients who developed loss of motion after arthroscopic anterior cruciate ligament reconstruction. Two hundred forty-four patients with a minimum followup of 1 year were reviewed. Loss of motion (defined as a loss of extension of more than 10 degrees or flexion of less than 125 degrees) was identified in 27 patients for an overall incidence of 11.1%. Factors associated with loss of motion included acute reconstruction (less than 1 month from initial injury), male sex, and concomitant medial collateral ligament repair or posterior oblique ligament reefing or both. Twenty-one patients required surgery to regain their motion; three patients required a second procedure. Twenty-one of 27 patients with loss of motion underwent a detailed followup and were compared with 24 randomly chosen controls who had a normal range of motion after anterior cruciate ligament reconstruction. At followup, patients who experienced loss of motion had a significant decrease in noninvolved to involved knee extension and flexion compared to the control patients. There was no difference between our patients and the controls regarding patellofemoral problems, anterior knee laxity, and functional strength. Sixty-seven percent of patients with loss of motion had a good or excellent result in comparison to 80% of the controls.