An athlete's desire to return to sport after anterior cruciate ligament (ACL) injury is a major indication for ACL reconstruction surgery. Typical clearance to return is 6 to 12 months postoperatively.To investigate the return-to-sport rate and participation level of a large cohort at 12 months after ACL reconstruction surgery.Case series; Level of evidence, 4.Data were analyzed for 503 patients who participated in competitive-level Australian football, basketball, netball, or soccer after ACL reconstruction surgery using a quadruple-strand hamstring autograft. Inclusion criteria included participation in competitive sport before the ACL injury and clearance from the orthopaedic surgeon to return to sport postoperatively. Patients completed a self-report questionnaire regarding preoperative and postoperative sports participation and the Cincinnati Sports Activity Scale. The International Knee Documentation Committee (IKDC) knee evaluation form and hop tests were used to evaluate knee function.Sixty-seven percent of patients attempted some form of sports activity by 12 months postoperatively; 33% attempted competitive sport. Of those who did not attempt any sports activity by 12 months, 47% indicated that they were planning to return. Men were significantly more likely than women to return. Patients who played sports with a seasonal competition, versus a year-round competition, were significantly more likely to return by 12 months. Patients with normal postoperative knee function (IKDC category A), versus those with nearly normal function (IKDC category B), were no more likely to return, but patients with good hop test results (≥85% limb symmetry index) were more likely to return than patients with poor results (<85%).People may require a longer postoperative rehabilitation period than that typically advocated to facilitate a successful return to competitive sport after ACL reconstruction surgery. The relationship between postoperative knee function and return-to-sport outcomes at 12 months after surgery was inconclusive.