PURPOSE: The purpose of this study was to determine the effects of fatigue on lower limb biomechanics during landing in patients who had undergone anterior cruciate ligament (ACL) reconstruction surgery. METHODS: Fifteen male participants who had undergone primary ACL reconstruction 15-19 months previously and 11 uninjured male control subjects had three-dimensional lower limb kinematics and kinetics quantified during single-limb landings, both before and during progression to fatigue. The single-limb landings were a vertical drop from a 30-cm platform, and subjects performed repetitive bilateral squats to induce fatigue. RESULTS: Fatigue led to reduced flexion in the lower limb, increased hip and knee abduction, increased knee rotation, and reduced knee joint moments. The response to fatigue was similar between the ACL-reconstructed limb and the control group as well as the reconstructed limb and the contralateral limb. The only kinematic variable to show a between-group or between-limb difference was hip flexion at initial contact, whereby flexion was greater for the reconstructed side. Although knee flexion and adduction moments were smaller for the reconstructed knee compared with the contralateral knee, they were not different from the control group. CONCLUSIONS: The results show that having an ACL reconstruction does not necessarily mean greater vulnerability to the effect of fatigue during single-limb landing. Nonetheless, some of the landing positions that were observed with fatigue potentially compromise the knee and integrity of the ACL graft.