We report a case of simultaneous anterior and posterior interosseous nerve syndrome in association with shoulder arthroscopy. Shoulder arthroscopy was performed in a 45-year-old male patient with left shoulder instability. In the right lateral decubitus position, under general anesthesia, traction was applied with elbow extension for 2 hours. One week after surgery, the patient revisited the clinic for weakness of the flexor of the thumb, index finger, and extensor of the fingers. Recovery was not achieved after four months of observation. Therefore, nerve exploration was performed in the anterior and posterior interosseous nerve and hourglass-like fascicular constriction was detected in the posterior interosseous nerve. The area of constriction was removed and epineural neurorrhaphy was performed. Three months after exploration, the extension function of the fingers was recovered. Recovery was achieved gradually, and, five months after nerve exploration, the symptoms were completely recovered. Simultaneous anterior and posterior interosseous nerve syndrome following shoulder arthroscopy is rare. However, it could occur due to the traction and position of the patient. Thus, the operator should be careful of traction and position of the patient.