Os acromiale is defined as the failure of fusion of one of the ossifications centers in the acromion. The mesoacromion is the most common location for this to occur. When this unfused portion is unstable, dynamic impingement results and is often associated with rotator cuff tears. Treatment of an unstable os acromiale remains under considerable debate. Numerous authors have reported on open reduction internal fixation, resection, and subacromial decompression, with varied results. Recently, arthroscopic management of the mesoacromion has been successful using a modified arthroscopic subacromial decompression technique. The surgeon must take care to ensure that the history, physical, radiographic, and arthroscopic examinations all correlate with the diagnosis. Strict surgical indications and meticulous technique can result in successful outcomes using arthroscopic techniques in the management of a symptomatic mesoacromion.