Background: Rockwood I and II acromioclavicular joint injuries are generally treated nonoperatively. The long-term outcome is considered to be good but has not yet been properly investigated. Purpose: To assess the long-term outcome after nonoperative therapy for Rockwood I and II acromioclavicular joint injuries regarding functional and radiologic outcome. Study Design: Cohort study; Level of evidence, 3. Methods: Eligible patients visited the emergency department between January 2003 and December 2015 and were ≥16 years old at the time of presentation. The main study parameters were the Constant score, the Disabilities of the Arm, Shoulder and Hand score, and the Simple Shoulder Test. The Constant score was measured in the injured and contralateral shoulders. Radiologic outcomes in both shoulders included joint displacement, joint space, degenerative changes, osteolysis of the distal clavicle, and ossification of the ligaments. Results: A total of 75 patients were included for follow-up. After a median follow-up of 85 months (interquartile range [IQR], 68.0-100.0), the mean Constant score in the injured shoulder for the total sample was 88.6 (SD, 12.7) as compared with 93.3 (SD, 8.7) in the contralateral shoulder, with a significant difference of 4.7 points between shoulders. The median Disabilities of the Arm, Shoulder and Hand score was 4.2 (IQR, 0.0-10.8), and the median Simple Shoulder Test was 100 (IQR, 91.7-100.0). The median patient satisfaction for the injured shoulder was 83 (IQR, 70.0-95.0). Regarding radiologic outcomes, for the injured shoulder versus the contralateral shoulder, patients had similar rates of degeneration (44% vs 46%) but more frequent osteolysis of the distal clavicle (31% vs 0%), ossification of the ligaments (29% vs 7%), and deformity of the distal clavicle (19% vs 0%). Conclusion: Despite the frequent occurrence of radiographic changes, long-term functional outcome after Rockwood I and II acromioclavicular joint injuries is good, with only clinically nonrelevant functional differences between the injured and contralateral shoulders.