We report a rare case of atypical Mycobacterium intracellulare infection encountered in a left sternoclavicular joint of an immunocompetent patient. The 34-year-old female patient presented with a one-year history of left sternoclavicular joint pain and swelling. The patient had multiple radiological investigations, which were suspicious for an infective cause. The patient had a biopsy of the joint, which returned showing acid-fast bacilli. The patient consequently received a prolonged course of medical treatment for M. intracellulare.