Purpose <p>To determine what variables are associated with loss of reduction of pubic symphysis injuries after plate fixation.</p> Methods <p>A retrospective review of patients treated with plate fixation of symphysis injuries was performed. Symphysis diastasis on injury, postoperative, and follow-up radiographs was measured. Associations between patient, fracture, and fixation characteristics and a loss of reduction ≥10 mm were analyzed.</p> Results <p>Fifty patients were included. The median age was 38.5 years (IQR 27.7 to 48.5), and a majority were male (80.0%, <i>n</i>=40). A loss of reduction ≥10 mm occurred in 18% (<i>n</i>=9), and revision fixation occurred in 6.0% (<i>n</i>=3). On univariate analysis, patients with a loss of reduction, compared to patients without, had a greater BMI (32.2 vs. 26.5, <i>p</i>=0.001), increased symphysis diastasis on injury radiographs (46.0 vs. 24.0 mm, <i>p</i>=0.0001), and more anterior pelvic space infections (55.6% vs. 14.6%, <i>p</i>=0.01). There were no associations between loss of reduction and age, AO/OTA classification, Young Burgess classification, 4-screw vs. &gt;4-screw plate fixation, number of posterior screws, or residual post-fixation symphyseal diastasis (<i>p</i>&gt;0.05). On multivariate analysis, initial symphysis diastasis was the only variable associated with loss of reduction ≥10 mm (<i>p</i>=0.03). A symphysis diastasis of ≥35.0 mm was found to maximize the sensitivity (88.9%) and specificity (75.7%) for identifying patients who had a loss of reduction.</p> Conclusions <p>The severity of initial symphysis diastasis was associated with loss of reduction. A threshold of 35.0 mm of symphysis diastasis maximized the sensitivity and specificity for identifying patients who experienced a loss of reduction.</p> Level of evidence <p>Retrospective comparative study, Level III evidence</p>