Introduction Acromioclavicular (AC) joint dislocations are common injuries accounting for 9–12% of all injuries to the shoulder girdle. This frequency is widely reported in the literature, but basic epidemiological features and sub-classification is not well investigated in a general urban population. The aim of the study was to investigate the incidence and epidemiology of acute AC joint dislocations in the capital region of Denmark

Materials and Methods All patients with acute AC joint dislocation admitted to the Emergency Departments at three University Hospitals serving a population of 549,225 residents in the Capital region of Denmark were prospectively registered from 1 January to 31 December 2019. Patients with trauma to the shoulder, pain from the AC joint and increased coracoclavicular distance on radiographs were included and classified according to Rockwood’s classification. Data on age, sex and mechanism of injury were registered.

Results 106 patients, male:female ratio 8.6:1, were included. Rockwood type III was the most common type accounting for 55.7% of the injuries. The overall incidence of AC joint dislocations was 19.3 per 100,000 person years at risk (PYRS). The age distribution was bimodal peaking at the ages of 20–24 and 55–59. The most common mechanism of injury was sports accounting for 80/106(75.5%) with cycling accounting for 51/106 (48.1%).

Conclusion Rockwood type III was the most common type of AC joint dislocation constituting 55.7% of the injuries. The incidence of AC joint dislocations was 19.3 per 100,000PYRS. Young and middle-aged males were at highest risk and most injuries occurred during sports.