BACKGROUND:Patients with bilateral anterior cruciate ligament (ACL) injuries tend to report worse results in terms of knee function and quality of life as compared with those with unilateral injury. There are limited data regarding return to preinjury sport in this group. PURPOSE:To report return-to-sport rates for patients who had bilateral ACL reconstruction and to compare outcomes according to age and sex. STUDY DESIGN:Case series; Level of evidence, 4. METHODS:A total of 107 patients (62 male, 45 female) who underwent primary ACL reconstruction surgery to both knees completed a detailed sports activity survey at a mean 5-year follow-up (range, 2.5-10 years). Follow-up also included the International Knee Documentation Committee subjective form, Marx Activity Scale, and Knee injury and Osteoarthritis Outcome Score-Quality of Life subscale. Rates of return to preinjury levels of sport were calculated for the whole cohort, and for further analysis, the group was divided according to age (<25 vs ≥25 years), sex, and time between the reconstruction procedures (<3 vs ≥3 years). RESULTS:The rate of return to preinjury sport after bilateral ACL reconstruction was 40% (95% CI, 31%-50%), as compared with an 83% (95% CI, 74%-88%) return rate after the first reconstruction procedure. Although not statistically significant, return rates were higher for male versus female patients (47% vs 31%) and older versus younger patients (45% vs 31%). Of those who returned to their preinjury levels of sport after the second reconstruction, 72% thought that they could perform as well as before their ACL injuries. In contrast, only 20% thought that they could perform as well if they returned to a lower level. Fear of reinjury was the most common reason cited for failure to return to sport after the second reconstruction. Patient-reported outcome scores were higher for those who returned to their preinjury levels of sport but did not differ for sex and age. CONCLUSION:Return-to-sport rates drop markedly after a second (contralateral) ACL reconstruction, with less than half of the investigated cohort returning to its preinjury level of sport. Return-to-sport outcomes are less than ideal for patients who have ACL reconstruction surgery to both knees.