Arthroscopic resection of the distal clavicle has been advocated as a surgical treatment option for acromioclavicular (AC) joint pathology. To our knowledge, iatrogenic fracture of the distal clavicle during distal clavicle resection has never been reported. This report describes distal clavicle fracture as a complication of misidentification of the AC joint and subsequent aggressive burring of the distal clavicle during shoulder arthroscopy. This case is further complicated by the development of symptomatic delayed union and adhesive capsulitis. Ultimately, a revision distal clavicle resection was performed, underscoring the fact that special care must be taken to properly identify the AC joint and rule out pre-existing distal clavicle stress fracture or osteolysis before performing the arthroscopic Mumford procedure.