Subcutaneous emphysema, pneumomediastinum, and tension pneumothorax are previously unreported complications of shoulder arthroscopy with subacromial decompression. Three patients developed extensive subcutaneous emphysema, pneumomediastinum, and bilateral tension pneumothorax during or immediately after shoulder arthroscopy with subacromial decompression. The procedure was terminated and appropriate treatment was given. All three patients recovered completely with no residual damage. The complications are thought to be associated with the extravasation of air that may be drawn in from the lateral portal when the arthroscopic infusion pump and power shaver with suction are turned on. Early diagnosis, followed by immediate termination of the infusion pump and suction shaver along with appropriate treatment can be life-saving.