To compare the time to return to sport (RTS) between patients who did and did not suffer a second anterior cruciate ligament (ACL) injury after ACL reconstruction. Etiology systematic review with meta-analysis. Cochrane Library, Embase, Medline, AMED, and PEDro databases were searched in August 2021 and again in November 2022. Clinical studies reporting time to RTS after ACL reconstruction and second ACL injury were eligible. We pooled continuous data (time months and proportions %), with random-effects meta-analyses. Pooled estimates were summarized in forest plots. A qualitative data synthesis was also performed. Twenty-one studies were included in the meta-analysis and 33 in the qualitative synthesis. Pooled incidence of second ACL injury was 16.9% (95% confidence interval CI: 12.8, 21.6). Patients who suffered a second ACL injury returned to sport significantly earlier (25 days; 95% CI: 9.5, 40.4) than those who did not suffer another injury. There was no difference in time to RTS for professional athletes who suffered a second ACL injury and those who did not. The certainty of evidence was very low. There was very low-certainty evidence that patients who suffered a second ACL injury had returned to sport 25 days earlier than patients who did not have another injury. For professional athletes, there was no difference in time to RTS between athletes who suffered a second ACL injury and athletes who did not. .