To evaluate whether augmenting traditional fixation with a femoral neck buttress plate (FNBP) improves clinical outcomes in young adults with high-energy displaced femoral neck fractures. Multicenter retrospective matched cohort comparative clinical study. Twenty-seven North American Level 1 trauma centers. Adult patients younger than 55 years who sustained a high-energy (nonpathologic) displaced femoral neck fracture. Operative reduction and stabilization of a displaced femoral neck fracture with (group 1) and without (group 2) an FNBP. Complications including failed fixation, nonunion, osteonecrosis, malunion, and need for subsequent major reconstructive surgery (early revision of reduction and/or fixation), proximal femoral osteotomy, or arthroplasty. Of 478 patients younger than 55 years treated operatively for a displaced femoral neck fracture, 11% (n = 51) had the definitive fixation augmented with an FNBP. One or more forms of treatment failure occurred in 29% (n = 15/51) for group 1 and 49% (209/427) for group 2 ( P < 0.01). When FNBP fixation was used, mini-fragment (2.4/2.7 mm) fixation failed significantly more often than small-fragment (3.5 mm) fixation (42% vs. 5%, P < 0.01). Irrespective of plate size, anterior and anteromedial plates failed significantly more often than direct medial plates (75% and 33% vs. 9%, P < 0.001). The use of a femoral neck buttress plate to augment traditional fixation in displaced femoral neck fractures is associated with improved clinical outcomes, including lower rates of failed fixation, nonunion, osteonecrosis, and need for secondary reconstructive surgery. The benefits of this technique are optimized when a small-fragment (3.5 mm) plate is applied directly to the medial aspect of the femoral neck, avoiding more anterior positioning . Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.