The best means of ensuring knee stability after anterior cruciate ligament (ACL) reconstruction remains a core debate in sports medicine.There is no difference between ACL reconstruction with patellar tendon or hamstring tendon autografts with regard to postoperative knee laxity and instability.Meta-analysis of individual patient data.Pooled analysis of individual patient data from 6 published randomized clinical trials included 423 patients with symptomatic unilateral anterior cruciate ligament injury randomly assigned to reconstruction with patellar tendon or hamstring tendon autograft. Knee instability, defined as a positive pivot-shift test result, was the primary outcome, and knee laxity, defined as a positive Lachman test result, was the secondary outcome. Odds ratios were computed before and after adjustment for potential confounders and trial effect. Regression analyses were performed to look for effects of covariates on outcomes, and mixed-effects models were used to account for a trial effect. Sensitivity analyses were conducted to explore the effects of missing data and excluding each trial.Anterior cruciate ligament reconstruction with patellar tendon autograft was significantly associated with a decreased risk of a positive pivot-shift test result (adjusted odds ratio, 0.46; 95% confidence interval, 0.24-0.86; P = .016). The risk of having a positive Lachman test result was not significantly different between the 2 groups. The estimated treatment effect was not substantially changed by differences in handling missing data or exclusion of any of the trials. A positive pivot-shift test result was more common in female (P = .003) and younger patients (P = .017).Postoperative knee instability was less common after ACL reconstruction with patellar tendon autograft than with hamstring tendon autograft.