Summary: No standard method for reporting tunnel widening after anterior cruciate ligament reconstruction (ACLR) has been reported. Some studies have shown no difference in tunnel widening with hamstring grafts versus bone-tendon-bone grafts. However, many studies have shown more widening with hamstring grafts. Fixation has been implicated as a cause of tunnel widening, but the literature does not offer conclusive evidence in this regard. Tunnel widening is finite and occurs in the first postoperative year. It has not been shown to progress after this time. No direct adverse event has been reported as a consequence of tunnel widening. However, revision ACLR may be made more difficult because of tunnel widening. This difficulty is greater when interference fixation is used and less great when cortical fixation is used. Various strategies, including increasing or decreasing postoperative motion, sealing off the tunnel, and bone grafting the tunnel, have been suggested; however, no consensus exists as to the best strategy.