Lipoma arborescens is a very rare intra-articular lesion characterized by villous lipomatous proliferation of the synovium, usually involving the knee joint. To date, in the literature, there has been only one reported case of lipoma arborescens in the glenohumeral joint. But, the authors treated the patient conservatively and reported only the magnetic resonance imaging (MRI) findings. We report a case of a patient with lipoma arborescens involving the glenohumeral joint. To our knowledge, this is the first reported case of lipoma arborescens involving the glenohumeral joint managed by arthroscopic synovectomy. We identified reactive bone erosions and arthritic changes in the humeral head in a 22-year-old male patient by arthroscopy.