This prospective observational study aimed to investigate the usefulness of the self-coiling catheter for continuous interscalene brachial plexus block (CISB) in patients undergoing arthroscopic rotator cuff repair (ARCR). In 22 patients, the self-coiling tip of catheter was placed anterior to the C5 and C6 roots under ultrasound guidance. The primary outcome is the relationship between the distance from the distal side pore of the catheter to the C5/C6 nerve roots and the visual analogue scale (VAS) of postoperative pain. The distance was recorded as a positive value when the distal pore was anterior to the C5/C6 nerve roots, and as a negative value when it was posterior to the roots. The median distance from the distal pore to C5/C6 nerve roots was 5.0 [4.1, 6.5] mm at catheter placement before surgery and 0.0 [- 4.3, 2.2] mm at catheter removal the day after surgery. The distance between the distal pore and the cervical nerve roots was associated with the VAS score at catheter removal (r =- 0.455, P = 0.033). These findings suggest that the distance between the distal pore of the self-coiling catheter and the C5/C6 nerve roots may affect the analgesic effect of CISB after ARCR.