A 47-year-old woman developed anterior interosseus nerve (AIN) syndrome after subacromial decompression and acromioclavicular joint resection. The operation was performed in the beach chair position and under general anaesthesia without the application of an interscalene block. Two weeks later, the patient presented with paresis of the distal interphalangeal joint of the second finger. Previous studies have proposed traction-type neuropraxia and extravasation of irrigation fluid as leading causes. Exploration and release of the AIN can be indicated if there is no improvement 3-6 months after the operation.