Objective To investigate the risk of new meniscal tears after treatment for anterior cruciate ligament (ACL) injury, in children and adults with and without ACL reconstruction. Design Prognosis systematic review (PROSPERO registration number CRD42016036788). Methods We searched Embase, Ovid Medline, Cochrane, CINAHL, SPORTDiscus, PEDro and Google Scholar from inception to 3rd May 2018. Eligible articles included patients with ACL injury (diagnosis confirmed by MRI and/or diagnostic arthroscopy), reported the number of meniscal tears at the time of ACL injury diagnosis/start of treatment and reported the number of new meniscal tears that subsequently occurred. Articles with fewer than 20 patients at follow-up, and articles limited to ACL revision surgery or multi-ligament knee injuries were excluded. Two independent reviewers screened articles, assessed eligibility, assessed risk of bias and extracted data. We judged the certainty of evidence using the Grading of Recommendations Assessment Development and Evaluation (GRADE) working group methodology. Results Of 75 studies included in the systematic review, 54 studies with 9624 patients and 501 new meniscal tears were appropriate for quantitative analysis. Heterogeneity precluded data pooling. The risk of new meniscal tears was 0%-21% when follow-up was <2 years, 0%-29% when follow-up was 2 to 5 years, 5%-52% when follow-up was 5 to 10 years and 4%-31% when follow-up was longer than 10 years. The proportion of studies with high risk of selection, misclassification and detection bias was 84%, 69% and 68%, respectively. Certainty of evidence was very low. Conclusion New meniscal tears occurred in 0%-52% of patients between 4 months and 20 years (mean 4.9 +/- 4.4 years) following treatment for ACL injury. The certainty of evidence was too low to guide surgical treatment decisions. This review cannot conclude that the incidence of new meniscal tears is lower if ACL injury is treated with surgery compared with treatment with rehabilitation only.