Background: To evaluate clinical and radiological outcome using AO hook locking plate in acute acromioclavicular joint injuries. Methods: This study was based on patients with Rockwood type 3 or 5 acromioclavicular joint injuries who received surgery with AO hook locking plate from June 2008 until June 2009. Among the 22 patients, 19 of them were male and 3 were female, the mean age was $44.4{pm}15.57$ years (20-72 years) and follow-up period was $15.5{pm}3.90$ months (12-23 months). Preoperatively, postoperatively, and at the final follow-up after the plate removal, both coracoclavicular distances were measured from the anteroposterior radiograph. Also, the Shoulder Rating Scale of the University of California at Los Angeles scores (UCLA scores), the American Shoulder and Elbow Surgeons scores (ASES scores), Constant scores, and the Korean Shoulder Society scores (KSS scores) were measured at the final followup to evaluate the function of the shoulder joint. Results: At the time of injury, the mean coracoclavicular distance of the injured side was $17.69{pm}4.23mm$ (9.57-27.82 mm) and the unaffected side was $7.55{pm}2.20mm$ (3.24-13.05 mm). The mean coracoclavicular distance measured postoperatively and at the final follow-up was $6.87{pm}2.34mm$ (4.07-14.13 mm) and $8.47{pm}2.96mm$ (4.37-17.48 mm), respectively. The mean UCLA, ASES, Constant, and KSS scores measured in the final follow-up were $33.5{pm}1.30$ (31-35), $90.8{pm}8.36$ (72-100), $78.6{pm}8.80$ (62-100), and $94.4{pm}5.08$ (84-100) each. Conclusions: From this short-term research, the surgical treatment using AO hook locking plates in acute acromioclavicular joint injuries is clinically and radiographically satisfying and considered as a useful treatment method.