CONTEXT: Low scores on psychological patient-reported outcomes measures, including the Anterior Cruciate Ligament-Return to Sport After Injury (ACL-RSI) and Injury-Psychological Readiness to Return to Sport (I-PRRS), after anterior cruciate ligament reconstruction (ACLR) have been associated with a maladaptive psychological response to injury and poor prognosis. OBJECTIVE: To assess the effect of time post-ACLR and sex on ACL-RSI and I-PRRS scores and generate normative reference curves. DESIGN: Case series. SETTING: Outpatient sports medicine and orthopaedic clinic. PATIENTS OR OTHER PARTICIPANTS: A total of 507 patients (age at ACLR, 17.9 ± 3.0 years) who had undergone primary ACLR and completed ACL-RSI or I-PRRS assessments ≥1 times (n = 796) between 0 and 1 year post-ACLR. MAIN OUTCOME MEASURE(S): An honest broker provided anonymous data from our institution's knee-injury clinical database. Generalized additive models for location, scale, and shape and generalized least-squares analyses were used to assess the effect of time post-ACLR and sex on ACL-RSI and I-PRRS scores. RESULTS: The ACL-RSI and I-PRRS scores increased over time post-ACLR. Males had higher scores than females until approximately 5 months post-ACLR, with scores converging thereafter. CONCLUSIONS: Males reported higher ACL-RSI and I-PRRS scores than females in the initial stages of rehabilitation, but scores converged between sexes at times associated with return to play post-ACLR. Normative reference curves can be used to objectively appraise ACL-RSI and I-PRRS scores at any time post-ACLR. This may lead to timely recognition of patients with a maladaptive psychological response to injury and a higher likelihood of a poor prognosis, optimizing ACLR outcomes.