BACKGROUND:Anterior cruciate ligament (ACL) injury has a significant psychological effect, and a negative psychological state is a commonly cited reason for a reduction or cessation of sports participation after ACL reconstruction (ACLR) surgery. PURPOSE:To identify factors that contribute to an athlete's psychological readiness to return to sport (RTS) after ACLR. STUDY DESIGN:Cross-sectional study; Level of evidence, 3. METHODS:A cohort of 635 athletes (389 male, 246 female) who underwent ACLR and had been cleared to RTS completed the Anterior Cruciate Ligament-Return to Sport After Injury (ACL-RSI) scale at an average 12 months (range, 11-24 months) after surgery. Demographics (age, sex), sporting outcomes (preinjury frequency), surgical timing (injury to surgery interval), clinical factors (laxity), functional measures (single-limb hop symmetry), and symptoms of pain and function (International Knee Documentation Committee subjective) were also taken, and univariate and multiple regression models were used to determine the association between these and the psychological readiness of the athlete to RTS (ACL-RSI scores). Data for the entire cohort were initially analyzed; then, patients were grouped according to whether they had returned to competitive sport, and the analysis repeated for each group (return/nonreturn). RESULTS:Univariate analysis for the entire group showed that all of the following had a positive effect on psychological readiness: male sex (β = 5.8; 95% CI, 2-10), younger age (β = -0.2; 95% CI, -0.4 to 0.01), a shorter interval between injury and surgery (β = -0.1; 95% CI, -0.1 to -0.02), a higher frequency of preinjury sport participation (β = 5.4; 95% CI, 2-9), greater limb symmetry (β = 0.5; 95% CI, 0.3-0.6), and higher subjective knee scores (β = 1.3; 95% CI, 1.1-1.4). In the multivariate model, subjective knee scores and age significantly accounted for 37% of the variance in psychological readiness ( r2 = 0.37, P < .0001). The only difference between the groups who had and had not returned to sport was that female sex was a significant contributor for the nonreturn group. CONCLUSION:Self-reported symptoms and function were most associated with psychological readiness to RTS after ACLR surgery. Male patients who participated frequently in sport before ACL injury had higher psychological readiness. Conversely, female patients had a more negative outlook and may therefore benefit more from interventions designed to facilitate a smooth transition back to sport.