BACKGROUND: Conservative treatment of posttraumatic antero-inferior shoulder instability leads to a high failure rate in a young and active population. However, treatment in an adolescent age group is not well documented.METHODS: We conducted a prospective study with adolescent patients (age 15 to 18 y) who suffered a first traumatic anterior dislocation of the shoulder. Two groups of patients were formed. The first group was treated with early arthroscopic stabilization and the second was treated conservatively. There were 43 shoulders in the operative group and 29 shoulders in the conservative group. The rehabilitation protocol was the same for both groups. All patients were followed up prospectively after 12, 24, and 36 months using Rowe Score.RESULTS: A total of 38 shoulders in the surgical group and 27 shoulders in the conservative group could be completely evaluated. From the conservative group, 19 patients (70.3%) suffered a recurrence of the instability. From the arthroscopic group, 5 patients (13.1%) suffered a recurrence of the instability.CONCLUSIONS: In an adolescent population (15 to 18 y), conservative treatment after first traumatic shoulder dislocation including immobilization in internal rotation leads to a significantly higher and unacceptable high failure rate compared with early arthroscopic stabilization.LEVEL OF EVIDENCE: Level II-prospective comparative study.