Objectives: Supracondylar humerus fractures are the most common elbow fractures seen in the pediatric population. The American Academy of Orthopedic Surgeons Board of Directors recently published clinical practice guidelines recommending surgical treatment for all displaced fractures. We sought to identify predictive factors to assist the orthopedic surgeon in identifying which type II fractures are more likely to fail closed reduction and immobilization without pinning.Design: This was a retrospective cohort study.Setting: This study was conducted at a pediatric medical center in the Midwestern United States.Patients: This study analyzed 29 patients who underwent closed reduction and immobilization for significantly displaced, type II supracondylar humerus fractures.Main Outcome Measurements: We compared the lateral capitellar humeral angle, Baumann angle, and anterior humeral line index at the time of presentation, postreduction, and at final follow-up.Results: Two statistically similar groups were identified based on the amount of initial displacement. Variables were examined between the 2 groups including age, gender, initial displacement, quality of initial reduction, treatment in cast or splint, and position of immobilization. Forty-eight percent of the patients failed closed reduction and immobilization, with an average 71% loss of initial reduction at final follow-up. None of the examined variables were statistically significant or had any predictive value for failure.Conclusions: Our study suggests that type II fractures should be viewed as a spectrum of injury. Our data show that a significantly displaced type II fracture that requires a reduction to obtain satisfactory alignment has a 48% chance of losing that reduction without percutaneous pinning.