Purpose <p>Nondisplaced femoral neck fractures (FNFs) in older adults are typically managed with internal fixation; however, fixation failure remains clinically significant. The Femoral Neck System (FNS) provides angular and rotational stability, but evidence in this population is limited. This study evaluated reoperation rates after FNS fixation and identified factors associated with reoperation.</p> Methods <p>This single-center retrospective cohort study included 103 patients aged ≥ 60 years with nondisplaced (Garden 1 and 2) FNFs treated with FNS during 2018–2024, all with ≥ 1-year follow-up. The primary outcome was reoperation for any cause. Clinical variables included age, sex, body mass index, American Society of Anesthesiologists Physical Status, and time to surgery. Radiographic parameters—Garden alignment index, posterior tilt (PT), and tip–apex distance—were assessed on preoperative and immediate postoperative radiographs. Receiver operating characteristic (ROC) analysis identified cutoffs, which were applied in multivariable logistic regression.</p> Results <p>Reoperation occurred in 14/103 patients (13.6%). Compared with the non-reoperation group, the reoperation group had longer time to surgery and greater preoperative and postoperative PT. ROC analysis yielded cutoffs of 46.4&#xa0;h (time to surgery) and 13.5° (preoperative PT). Multivariable logistic regression showed that time to surgery ≥ 46&#xa0;h (OR 15.10) and preoperative PT ≥ 14° (OR 3.64) were independently associated with reoperation. Patients meeting both cutoffs had a 44.4% reoperation rate compared with 2.4% among those meeting neither.</p> Conclusion <p>Time to surgery ≥ 46&#xa0;h and preoperative PT ≥ 14° were independent predictors of reoperation after FNS fixation in older adults with nondisplaced FNFs.</p>