In a prospective study, 60 patients with acute acromioclavicular dislocation were randomly allocated to treatment with a broad arm sling or to reduction and fixation with a coracoclavicular screw. Of these 54 were followed for four years. Conservatively-treated patients regained movement significantly more quickly and fully, returned to work and sport earlier and had fewer unsatisfactory results than those having early operation. For severe dislocations, with acromioclavicular displacement of 2 cm or more, early surgery produced better results. Conservative management is best for most acute dislocations, but younger patients with severe displacement may benefit from early reduction and stabilisation.