BACKGROUND: Following anterior cruciate ligament (ACL) reconstruction, children are at significant risk for complications, including contralateral ACL rupture. The purpose of this study is to determine which children are at risk for a contralateral ACL tear after ipsilateral reconstruction. METHODS: After review of medical records, we contacted patients who underwent primary ACL reconstruction between 2009 and 2016. Patients were included in the study if they were able to provide follow-up data either in person or remotely at least 2 years after surgery. Demographic data, sports participation, and intraoperative findings and techniques were recorded. All patients were also asked to confirm returning to sport information and postoperative complications (including contralateral ACL tear). Univariate analysis consisted of χ and independent samples t tests. Purposeful entry logistic regression was then conducted to control for confounding factors. Kaplan-Meier analysis was performed to assess contralateral ACL survival. RESULTS: A total of 498 children with average follow-up of 4.3±2.1 years were included in the analysis. The mean age was 15.0±2.3 years and 262 patients (52.6%) were female. Thirty-five subjects (7.0%) sustained a contralateral ACL tear at a mean of 2.7±1.7 years following index reconstruction. Kaplan-Meier analysis revealed the median contralateral ACL survival time to be 8.9 years [95% confidence interval (CI): 8.3, 9.5 y]. In univariate analysis, 11.5% of female patients had a contralateral rupture compared with 2.1% of male patient (P<0.001). Patients with a contralateral tear had a mean age of 14.4±2.0 years compared with 15.1±2.3 years for those without an ACL injury in the opposite knee (P=0.04). After controlling for numerous factors in a multivariate model, female patients had 3.5 times higher odds of sustaining a contralateral ACL tear than male patients (95% CI: 1.1, 10.6; P=0.03). Each year of decreasing age raised the odds of contralateral injury by a factor of 1.3 (95% CI: 1.1, 1.6; P=0.02). Furthermore, children younger than 15 years had 3.1 times higher odds of contralateral rupture than those aged 15 and older (95% CI: 1.3, 7.2; P=0.01). CONCLUSIONS: After adjusting for confounding factors in a multivariate model, female patients were at increased risk of contralateral ACL tear following ipsilateral reconstruction, as were younger children. Specifically, ACL rupture in the opposite knee was more likely in patients below the age of 15 years. LEVEL OF EVIDENCE: Level III-prognostic study.